Language Point 7

Psychologist Arthur F. Kramer tested volunteers working on arithmetic problems (Para. 7)

Meaning: Psychologist Arthur F. Kramer tested willing persons who were trying to solve arithmetic problems

volunteer: n. person who offers to do something without being forced

This is a huge project, but we have a lot of volunteers for the most difficult work.
這是一個大項目，但我們擁有許多志愿者來承擔其中最困難的工作。

After the dancing party, quite a lot of young men stayed behind as volunteers to clean the place.
舞會之后，許多年輕人自愿留下來打掃場所。

work on (upon): have (something) as the subject of thought or effort

The scientists are still working on inventing new methods of reaching outer space.
科學家仍在努力探索進入外層空間的新方法。

Is Tom still working on the new book that he promised?
湯姆還在寫那本他答應寫的書嗎？