Question: Who did contestants have to perform in front of in order to receive their next clue?
About the article "The Amazing Race 21", section "Leg 7 (Turkey → Russia)".

Candidate passages:
A team of two contestants, always in the studio, had to use a library of (deliberately relevant) maps and reference materials to solve up to five clues, and communicate instructions via a radio link to a "skyrunner" who had the use of a helicopter.
The contestants were given the first clue for free, the solving of which would lead to the location of the second clue and so on until a trinket or other significant object was found by solving the final clue.
The contestants won a higher cash prize each time they solved a clue correctly.
This was all done "against the clock".
Even once the contestants had solved the final clue, the skyrunner still had to confirm they were correct, by reaching the final target.
On a few occasions, the contestants solved all five clues with time to spare, in which case, a bonus clue was given to the contestants.
This typically resulted in their winning a bottle of champagne.
One such occasion was the North Yorkshire episode (4.10), in which the bonus clue instructed them to go to "Great British Hospital X-ray Unit".
This was actually code for "return to the helicopter, registration G-BHXU", but Anneka alarmed the passers-by outside Skipton Castle by frantically asking "which way to the hospital?
"Understandably, the skyrunner and helicopter did not have freedom to fly and land anywhere they wished.
Although the pilot could to an extent request permission from airspace authorities to fly off-course, as happened on occasions, landings needed to be agreed in advance with landowners of a suitable location near the clue.
On occasions the helicopter would land in a clearly marked out area, especially at public places.
It is open to interpretation how much detail of the route was known in advance by either of the studio presenters or even the skyrunner herself, and hence to what extent the contestants were helped to correctly direct the skyrunner to the approximate location.
Kenneth Kendall has always stressed that he did not know the clues and locations in advance, and any help that he gave the contestants was from his own knowledge.
According to a "making of "Treasure Hunt"" programme, Anneka Rice was confined to the hotel on the day that the cameraman, video recordist and helicopter pilot undertook a rehearsal (typically the day before the programme was recorded), so she had no advance knowledge of the locations.
This did not stop her carrying out research about the general area in order to have a stock of interesting facts to fill in any awkward silences that might arise while the contestants were thinking. 
Airdate: December 2, 2012  Amsterdam (Amsterdam Airport Schiphol) to Barcelona, Spain (Barcelona–El Prat Airport)  Barcelona (Port of Barcelona) to Palma, Mallorca (Port de Palma /Puerto de Palma de Mallorca ) Dalt Murada, Palma (Palma Cathedral) Manacor (Centro de Alto Rendimiento)  Campanet (Coves de Campanet /Cuevas de Campanet )  Sa Pobla (Windmill) "or" Muro (Plaza de Toros la Monumental) Palma (Bellver Castle)  In this Leg's Roadblock, one team member had to return 20 tennis balls fired by an automatic server within the bounds of a clay court in order to receive their next clue.
If the machine ran out of tennis balls, they would have to start the task over, their prior count reset.
The Detour on this Leg was a choice between Spin It and Bull It.
In Spin It, teams donned safety gear and then replaced two blades on a 400-year-old Mallorcan windmill.
Once a mechanic checked their work, they received their next clue from a pair of Don Quixote and Sancho Panza impersonators.
In Bull It, the team would wear a special two-person bull outfit, with the person in front unable to see where they were going.
The team member in back would verbally guide their partner in the front to circle eight matadors and then strike a target of a ninth to launch a final dummy matador.
The entire course had to be completed within two minutes for the team to get their next clue.
Additional tasks:  At the Palma Cathedral, teams had to search amongst a small troupe of actors dressed up as devils and demons participating in a performance for "La Nit del Foc", a traditional Mallorcan festival, for one who was holding their next clue.
At the Coves de Campanet, teams were instructed to follow the music in the caves to their next clue, leading them to a pair of guitarists.  
Air dates: November 20 – 22, 2012  Angeles (Holiday Inn Clark)  Mabalacat (Mabalacat Bus Terminal) to Legazpi, Albay (Grand Central Terminal)  Daraga (Red Labuyo Restaurant)  Daraga (Cagsawa Ruins)   Legazpi (Ligñon Hill – World War II Japanese Tunnel)  Legazpi (Mt.
Mayon – Lava Wall at Bonga Gully)  Legazpi (Legazpi Boulevard – Breakwater)  In this leg's Detour, teams had to choose between "Jig" or "Pig".
In "Jig", teams would have to don costumes and perform a traditional Ibalong dance to the satisfaction of two judges.
In "Pig", teams would have to cover each other in mud and powder and enter a muddy pen to catch four pigs.
Once each team member caught two pigs and put them in another pen, a farmer would give them their next clue.
In this leg's Roadblock, teams have to pick one luggage among those that they had brought with them at the start of the Leg.
They would then ride an all-terrain vehicle to deliver that one luggage to a local chieftain who would open it for them.
If they pick the luggage without the clue, they would have to go back to their partners and choose another luggage until they find the one with their next clue.
Additional tasks  Teams had to ride a marked jeepney in order to travel to all the race locations of this leg.
From the start of the leg at the Holiday Inn Clark, teams had to carry eight luggages all the way to the Pit Stop.
At Red Labuyo Restaurant, teams had to eat a bowl of Bicol Express and a bowl of strawberry ice cream to receive their next clue.
At the World War II Japanese Tunnel, teams had to find their next clue which was hidden inside a box.  
Airdate: November 1, 2009  Dubai (Dubai International Airport) to Amsterdam, The Netherlands (Amsterdam Airport Schiphol) Afsluitdijk (Cornelis Lely Monument) Groningen (Martinitoren)  Vierhuizen , De Marne (Windmill De Onderneming )  Zoutkamp (Harbor)  In this leg's Roadblock, one team member had to climb to the top of the Martinitoren and count all of the bells in the carillon.
When they gave the right number (62) to the carillonneur, they would receive their next clue.
If they provided the wrong number, they would have to climb back up to the carillon to count again.
In this leg's Detour, teams chose between Farmer's Game or Farmer's Dance.
In both Detours, teams dressed in traditional Dutch costumes—one male and one female—and rode bicycles to their Detour choice.
In Farmer's Game, teams had to strip down to their Dutch underwear and swim across a creek.
On the other side, they had to retrieve a special set of golf clubs and play 3 holes of Farmersgolf.
Team members took turns with each stroke and had to finish within par of 8 strokes on each hole to receive their next clue.
In Farmer's Dance, teams had to find a country festival where one team member had to hit the bell on a high striker (if that team member failed, team members would take turns until they hit the bell).
They then had to enter a dance hall to learn a traditional Dutch folk dance and perform that dance in front of a crowd.
If the dance was to the instructor's satisfaction, the instructor would give each team member a serving of soused herring which they had to eat in order to receive their next clue. 
Airdate: 14 August 2012  Banff to Calgary (Calgary International Airport)  Calgary (Calgary International Airport) to Beijing, China (Beijing Capital International Airport) Beijing (Ghost Street [])  Beijing (Wuzhisheng Foot Reflection Health Center) Beijing (Marco Polo Bridge)  Great Wall of China (Mutianyu) Beijing (Forbidden City — Tàimiào Temple)  In this Leg's Detour, teams had to choose between Waiter or Wheel.
In Waiter, teams had to take food orders from customers in a restaurant in Mandarin Chinese and recite each order to the chef.
If they pronounced the orders correctly, the chef would give them the meals to serve to the customers.
Once every customer on the table received their meal, they would receive their next clue.
In Wheel, teams had to spin a wheel with different Chinese delicacies on it, and then eat the dish the wheel stopped on.
After each team member had eaten two dishes, they would receive their next clue.
In this Leg's Roadblock, teams travelled to the Mutianyu section of the Great Wall of China where one team member had to figure out how to pass through 9 rows of warriors who were guarding their next clue.
In each row of warriors, only one warrior would let them through and the others would block them.
If the team member was blocked by a warrior 3 times, they would have to go back to the first row and start again.
Once they passed through all 9 rows, they would receive their next clue.
Additional Tasks At the Wuzhisheng Foot Reflection Health Center, each team member received a continuous 10 minute foot massage, 5 minutes for each foot, to receive the next clue.
If they asked to stop the massage, they would have to start the minutes again.
At the Marco Polo Bridge, teams had to count the number of lion head statues.
If they were correct they received their next clue.