They left a boy to answer the bell.

他们留下一个孩子应门。

youdao

I rang the bell, but there was no answer.

我按了门铃，但没有人应门。

《牛津词典》

Suddenly, I know all the answer, but the bell rang.

突然之间，我知道了所有题目的答案，但是铃声响了。

youdao

On the first morning I am among just seven passengers who answer the bell at breakfast.

FORBES: Go with the Floe

"The one way you can't win a race is to quit it, and until somebody beats me, I'm going to answer the bell for every round of this fight, " he said.

NPR: Solid Wins for McCain; Clinton, Obama Close

In that moment, Bell knew the answer to the puzzle of the harmonic telegraph.

NEWYORKER: In the Air