我们不得不把整首诗背下来。

We had to learn the whole poem off ___by ___heart.

我把他所有的歌都背下来了，而且我一直在唱。

I know all his songs ___by ___heart and I was singing all the time.

她能背下整个剧本。

She can recite the entire script ___by ___heart.