【题目】His friends as soon as they knew he had recovered from illness(cheer)
一知道他恢复了健康，他的朋友就高兴起来。

【答案】cheered up
【解析】cheer up固定短语“振作起来，高兴起来”，根据as soon as they knew he had recovered from illness的时态。可知谓语动词用一般过去时，因此答案为cheered up。