--What is that on the table?Oh a set of on the table.A. key isB. keys are C. keys is

问题补充：

--What is that on the table? --Oh, a set of on the table.

A. key is

B. keys are

C. keys is

D. key are

答案：

A. key is

B. keys are

(答案→)C. keys is

D. key are

解析：句意：桌子上是什么？——是一套钥匙在桌子上。结合语境可知本句中钥匙应该用复数形式，本句中实际主语是a set故谓语动词用单数，选C。