问题补充：
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：
A. is not
B. hasn’t been
(答案→)C. was not
D. hadn’t been
解析：
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
