1（2011北京卷）23. Tom __________ in the library every night over the last three months.
A. works B. worked C. has been working D. had been working
【解析】选C。考查时态。
2. His sister left home in 1998, and ________ since.
［2009全国卷Ⅰ，26］
A. had not been heard of B. has not been heard of
C. had not heard of D. has not heard of
