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.

志愿者们在公园里种树，美化社区环境。

The ___volunteers planted trees in the park to beautify the neighborhood.

他自愿帮助清理公园的垃圾。

He ___volunteered to help clean up the park.