1. They ______ on the program for almost one week before I joined them, and now we _____on it as no good results have come out so far.
A. had been working; are still working B. had worked; were still working
C. have been working; have worked D. have worked; are still working
此题的时间参照点是before I joined them,，所以第一个空应该用过去完成进行时，第二个空根据时间now用现在进行时。
2. It would be a good idea to use a plastic bottle, ___cut off, as a container to grow young plants in.
A. of which the top B. the top is C. the top of which D. with its top
此题是独立主格结构，如果题干改为 ____is cut off,答案则为A或C
