Isn't it time you got down to the papers?A. markB. be markedC. being markedD. marking

问题补充：

Isn it time you got down to the papers?

A. mark

B. be marked

C. being marked

D. marking

答案：

A. mark

B. be marked

C. being marked

(答案→)D. marking

解析：“got down to”中的“to”是介词，因而要用动名词作宾语，而动名词“marking”与其逻辑主语“you”是主动关系。