The poor boy could do nothing but at the corner of the street.A. to sitB. sittingC. sitD.

问题补充：

The poor boy could do nothing but at the corner of the street.

A. to sit

B. sitting

C. sit

D. sat

答案：

A. to sit

B. sitting

(答案→)C. sit

D. sat

解析：介词but前面有实义动词 do时，其后要跟没有 to的不定式，即直接跟动词原形。