wish I ____ busy yesterday or I _____ you with the problem.
A.wasn't;could help
B.hadn't been; would help
C.hadn't been;could have helped
D.wasn't;would have helped
应该选哪个，这个真感到奇怪，我看到yesterday，就想到是要用一般过去式。可答案不是用过去完成时。怎是怎么说的呢，还后面的一空更不懂的解释了。
关键是虚拟语气为什么就选C？