问题补充：
If it had been possible, I would have helped him, but I too busy.
A. had been
B. would be
C. were
D. was
答案：
A. had been
B. would be
C. were
(答案→)D. was
解析：句意：如果可能的话，我肯定会帮助你的，但是我太忙了。对过去的虚拟If+主语+had +动词过去分词,主语+would / should / might / could have + 动词过去分词。所以描述的是过去的事情，故我过去很忙应该用过去时。
