问题
选择题
Jack could have avoided that terrible car accident, but he ________ careful enough.
A．is not
B．hasn’t been
C．was not
D．hadn’t been
答案
答案：C
这题考查时态，句意是：杰克本来可以避免这场可怕的车祸，但是他太不仔细了。从could have done看出是“过去本可以做…却没有做”，那不够仔细是过去的事实，所以选C