i would have gone to visit him had it been at all possible,b

題目：

i would have gone to visit him had it been at all possible,but i __ fully occupied last week.
A.was B.had been
had it been是虛擬if 省略的倒裝嗎?

解答：

你說的對,had it been是虛擬if 省略的倒裝,but後面陳述的是 last week的一個狀態,所以選A