—Are these buses? —Yes A. it is B .these are C. they are.

问题补充：

—Are these buses?

—Yes,

A. it is B .these are C. they are.

答案：

解析：句意：——这些是公共汽车吗？——是的，他们是。A. it is 它是， B .these are这些是； C. they are.他们是。在英语中代替these或those用代词they.故选C。