You are given a paragraph, a question and some answer options (associated with "A", "B", "C", "D", etc.) You need to list all the correct answer options with their associated letters (e.g. "A" can be a valid answer). Note that sometimes, more than one option can answer the question correctly and completely. In those cases, please generate all such options separated by a comma (e.g. "A, B" is a valid answer). Do not generate anything else apart from one or more of the following characters: 'A', 'B, 'C', 'D', etc.

Example Input: Paragraph- Sent 1: (CNN) -- English club Chelsea have completed the signing of Oriol Romeu from Spanish and European champions Barcelona.
Sent 2: The 19-year-old is currently playing for Spain at the World Under-20 Championships in Colombia and has signed a four-year deal with last season's Premier League runners-up.
Sent 3: The deal is worth $7 million and includes a buy back clause, set at $14 million after the first year and $21 million after the second.
Sent 4: Romeu started his career at Barcelona's city rivals Espanyol before joining the Camp Nou academy in 2004.
Sent 5: The midfielder, who can also play in central defence, made his debut for Barcelona in last season's Spanish Supercup match with Seville and got his first taste of league action against Deportivo in May 2010.
Sent 6: He has played 90 minutes in both of Spain's games at the World Under-20 Championships, when they beat Costa Rica and Ecuador.
Sent 7: Chelsea official web site confirmed the signing and said Romeu is "renowned for his strength and his expansive passing ability."Sent 8: Another player leaving Barcelona is Jeffren Suarez after he agreed to join Sporting Lisbon.
Sent 9: The Portuguese outfit have paid $5 million for the 23-year-old which, like the Romeu deal, includes a buy back option.
Sent 10: Jeffren joined Barca from Tenerife in 2004 and made his debut for the Catalan club in the 2006-07 season.
Question: What position did Romeu play when he started his career at Barcelona's city rivals Espanyol? (A) Goalie (B) Midfielder (C) Forward (D) Central defence (E) Mid fielder (F) Wing.
Example Output: B, E.

Example Input: Paragraph- Sent 1: Conduction is the transfer of thermal energy.
Sent 2: It occurs between objects or substances that are touching.
Sent 3: Thermal conductors are materials that are good conductors of heat.
Sent 4: Thermal insulators are materials that are poor conductors of heat.
Sent 5: Both conductors and insulators have important uses.
Sent 6: Convection is the transfer of thermal energy.
Sent 7: This occurs as particles move within a fluid.
Sent 8: The fluid may be a liquid or a gas.
Sent 9: The particles within the fluid transfer energy by moving from warmer to cooler areas.
Sent 10: They move in loops.
Sent 11: These loops are called convection currents.
Sent 12: Radiation is the transfer of thermal energy by waves.
Sent 13: These waves can travel through empty space.
Sent 14: When the waves reach objects, the heat is transferred to the objects.
Sent 15: Radiation is how the Sun warms the Earths surface.
Question: In order for Convection to happen, should you use a conductor or an insulator? (A) An insulator (B) A conductor because insulators are bad conductors of heat (C) A conductor.
Example Output: B, C.

Example Input: Paragraph- Sent 1: Force is a vector.
Sent 2: What then is a vector?
Sent 3: Think about how you would give directions to a friend.
Sent 4: You would not say, just walk half a mile.
Sent 5: The person may walk a half mile in the wrong direction!
Sent 6: More information is needed.
Sent 7: You may say, follow this particular road for a half mile.
Sent 8: You may say, look for the green house on Sumter St. In both examples, you provided a direction.
Sent 9: You also gave the distance.
Sent 10: In other words, you provided a vector.
Sent 11: You did not just give a distance.
Sent 12: Both pieces of information are needed to find a location.
Sent 13: This is just like describing forces.
Sent 14: To explain forces, both size and direction are needed.
Sent 15: Notice the girl in Figure 1.1.
Sent 16: She is pushing the swing away from herself.
Sent 17: Thats the direction of the force.
Sent 18: She can give the swing a strong push or a weak push.
Question: When you say, "Follow this particular road for a half mile," what kind of information are you providing in addition to distance? (A) Direction (B) Force (C) Energy (D) Motion.
Example Output:
A.