Before __ the trunk must be checked.
A.used
B.to use
C.being used
D.to be used
答案:C
There _____an old tree here. I wonder how they could manage to remove such an old tree.
A.seemed not
B.not seemed
C.didn’t seem to be
D.didn’t seem to have
如果把打气筒的出气口封住,在活塞下压的过程中,被密闭的气体的质量 _________ ,体积 _________ ,密度 _________ .(填变大、变小或不变)