[译] 大多数学生都积极参加课外活动。
[误] Most students actively take part in extracurricular activity.

[正] Most students actively take part in extracurricular activities.
[注] activity 在表示“所做或待做的事情、活动”时，是可数名词，且常常用复数形式。而在表示“活动的状态、活力”时是不可数名词。再如：When a man is over seventy, his time of full activity is usually past. 当人活到七十岁以后，他充满活力的时期通常都已过去。