他自愿帮忙打扫公园。

He ___volunteered to help clean up the park.

许多志愿者在社区中心免费教授英语课程。

Many ___volunteers teach English classes for free at the community center.

她主动提出可以帮忙照顾小孩。

She ___volunteered to help take care of the kids.

他18岁时自愿参军。

He ___volunteered for the army when he was 18.