请教一道英语题

Question

I would have gone to visit him in the hospital had it been at all possible, but I ______ fully occupied the whole of last week.
A. were b. had been C. have been D. was
参考答案为D,请教高手为什么选D?谢谢！
不好意思参考答案为B,请教高手为什么选B?谢谢！

Answer 1

因为前面有个had，所以要用过去时，而与I搭配的是was，所以就选d啦

Answer 2

从last week得知这是上周发生的事情，过去发生的事，用一般过去时态即可。

Answer 3

首先这是一个对过去的虚拟。
说如果我以前可能我就去医院看他，但我上周太忙了。言外之意就是说没去。
would have done是表示对过去的虚拟。
因为是have done.
要是would do就是现在了。

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难道是因为虚拟语气才填had been？
我学业不精|||

Answer 4

last week 表示过去式，I只和am连用，am的过去式是was,所以选D

Answer 5

前半句是条件，没影响“but”后边的。
the whole of last week可以理解为上星期，泛指一个时间点。

时间久了，不知道能不能说的让你明白。