— is this? Is it a ruler?—Yes it is a red ruler.A. HowB. WhoC. WhatD. What color

问题补充：

— is this? Is it a ruler?

—Yes, it is a red ruler.

A. How

B. Who

C. What

D. What color

答案：

A. How

B. Who

(答案→)C. What

D. What color

解析： 回答语表示的事物，对事物提问的用what，故本题选C。