1.Tom did nothing but take back __back what he had said.A.to take B.take

1.Tom did nothing but take back __back what he had said.A.to take B.take
2.Now we could no to do anything but__for him here.
A.wait B.to wait
我们老师说有do没to 有to没do...那为什么这两道题答案都是do呢?