By the late 1970s,

A) Russia began reforms which eventually transformed it to a more market-oriented economy.
B) China began reforms which eventually transformed it to a more market-oriented economy.
C) Russia and China were both quickly becoming market-oriented economies.
D) None of the choices are true.

By the late 1970s, China began implementing economic reforms under the leadership of Deng Xiaoping, which gradually shifted the country towards a more market-oriented economy. Russia, on the other hand, did not begin implementing significant economic reforms until the 1990s, after the collapse of the Soviet Union. Therefore, option B is the correct answer.