she would go and inform him if she ___ his address. A know B had known C knew D would have known

if sb had done ... , ... would have done
if sb did/ were ... , ... would do ....
这种形式才对啊

说得好
这是错综条件句
结果主句和条件从句的谓语动作若不是同时发生时，虚拟语气的形式应作相应的调整。
从句的动作与过去事实相反，而主句的动作与现在或现在正在发生的事实不符
eg：
If I had worked hard at school,I would be an engineer,too.
如果我在学校学习刻苦的话，我现在也会成为一个工程师了
If they had informed us,we would not come here now.
如果他们通知过我们的话，我们现在就不会来这里了

相信你能明白了吧