About six months later the letter they were looking forward to at last．A. arrivedB. arriv

问题补充：

About six months later，the letter they were looking forward to at last．

A. arrived

B. arriving

C. had arrived

D. arrive

答案：

(答案→)A. arrived

B. arriving

C. had arrived

D. arrive

解析：考查动词时态。look forward to中的to是介词，而不是不定式符号，所以后接动词作宾语时，要用动名词，而不用动词原形。