Question: In 2006, for emissions reasons, India Yamaha Motor replaced its RX 100 two-stroke motorcycle with the Yamaha Crux. What type of engine does the Crux have?

Context paragraphs:
Yamaha RX 100: The Yamaha RX100 is a 98 cc two-stroke single-cylinder air-cooled motorcycle that was manufactured between 1984 and 1996 in India.

Yamaha RX 115: The Yamaha RX 115 is a standard motorcycle with a 115 cc two-stroke engine manufactured by Yamaha Motor Company.  Debuted in 1981, the RX 115 is popular in Malaysia, Thailand, Pakistan, Turkey, Uruguay, Singapore, Venezuela, Colombia, and Dominican Republic.

Yamaha RZ350: Yamaha RZ350 (RD350LCII) (liquid cooled) is a motorcycle powered by a twin-cylinder two-stroke engine, reed valved 347 cc engine.  The bore and stroke are 64 x .  Coming out in 1983, it was the evolution of Yamaha's popular and well known RD350 (1972–75) and RD350LC (1980–86).  Production was carried on into the 1990s and a different version with no YPVS power valve in the engine was used in Yamaha's Banshee ATV until its final model year in 2006 in the United States.  Yamaha Motor sold the Banshee in Canada until 2008.  There were several other models, the 1985 RZ350F, 1986-92 RZ350F2,N,NF, and the 1992-5 RZ350RR were produced in Brazil.  The picture shown to the right is a model with an aftermarket, "Expansion Chamber" higher flowing, high-performance exhaust system, devoid of the catalytic converter and other exhaust pollution control items.

Yamaha SS 125: The Yamaha SS 125, is a rechristened version of Yamaha Gladiator, is a 125 cc motorcycle, produced by India Yamaha Motor.

Yamaha Fazer (India): The Yamaha Fazer is a motorcycle produced by India Yamaha Motor, a subsidiary of Yamaha Motor Company.

India Yamaha Motor: India Yamaha Motor Private Limited (IYM) is the wholly owned Indian subsidiary of Yamaha Motor company, Japan Joint-investor with Mitsui & Co., Ltd.  Yamaha Motor Company,Japan made its initial foray into India in 1985 as a joint-venture with Escorts Group.  In August 2001, it became a 100% subsidiary of Yamaha Motor Co., Ltd, Japan (YMC).  In 2008, Mitsui & Co., Ltd. entered into an agreement with YMC to become a joint-investor in India.  It produces a range of motorcycles for domestic consumption and export including the FZ, SZ, Saluto, Fazer, and YZF.

Yamaha FZ750: The Yamaha FZ750 is a sports motorcycle produced by Yamaha Motor Corporation between 1985 and 1991.  The FZ750 is notable for several reasons, perhaps the most radical being the 5-valve cylinder head with a radial arrangement.  This became something of a Yamaha trademark, and although disputed in recent years, it was argued that for a given lift, the 3 inlet valves flowed more efficiently than conventional twin inlet valves.  What was indisputable was that their light weight allowed for faster opening speeds, and softer valve springs, all contributing to theoretical increases in engine speed and thus power outputs.  Whatever the scientific merits, the bikes were famous for their linear power delivery, and in 1985 it was still considered impressive to achieve 150mph from a 750 road machine.  Yamaha also designed the motor to have a forward-inclined cylinder block, to effectively lower the centre of gravity.  As a result, the FZ750 ran a relatively long wheelbase, which hampered it when used for road racing.  What was clear was that Yamaha had considered the engine design in the overall package, rather than as had happened before, when engines were created, and then somehow bundled into a chassis.  The FZ750 show-cased Yamaha's design skills.

Yamaha Libero (G5): The Yamaha Libero G5 is a 106 cc, single-cylinder four-stroke motorcycle from India Yamaha Motor.  Its predecessor was known as just Yamaha Libero.  Unlike Libero G5, Libero had tachometer and round headlights but lacked fuel gauge.  However, Libero G5 came with a sporty headlight and fuel gauge, but lacked the tachometer.  A new set of air scoops with a honeycomb grille do dual duty; directing airflow over the engine block and also neatly covering the gap between the engine and the fuel tank.  The Libero G5’s frame continues to be the tubular dual-cradle type.

Yamaha Crux: The Yamaha Crux is a 106 cc, single-cylinder four-stroke motorcycle made by India Yamaha Motor.  The Crux is designed for Indian markets.  It was launched in 2004 replacing RX 100, as 2-Stroke engines were not able to meet government's emission norms.

Yamaha RS-100T: Yamaha RS-100T Torque induction series, also known as RS-100 series, is a series of two-stroke motorcycle models manufactured by Yamaha Motors Co. Ltd as a successor of the Philippines' most popular 2T motorcycle/tricycle model.  It debuted in 1977 especially for the Asian market.  While the older Yamaha RS-100 uses a pressed steel frame that also acts as the main body, the RS-100 uses steel tubes for the frames and metal cover sets for the body.

Supporting paragraphs: Yamaha Crux Yamaha RX 100
Answer: four-stroke