语法填空：如果我知道那天是你生日

填空：对方的生日已经过去，说话人当时不知道，也没买贺卡，现在表示遗憾。

I'm sorry! If I ____ it was your birthday yesterday, I would _______ a card for you!

a) knew, buy
b) had known, buy
c) had known, have bought

你知道答案吗？