他自愿帮助清理公园的垃圾。

He ___volunteered to help clean up the trash in the park.

她每周都会去养老院做志愿者，陪伴老人们聊天。

She goes to the nursing home as a ___volunteer every week to chat with the elderly.

她大学毕业后自愿参军。

She ___volunteered for military service after graduating from college.

还没等我问，她就主动提供了解决方案。

She ___volunteered the solution before I could even ask.