1. 不可数名词：活动性；活力
2. 不可数名词：繁忙的或充满活力的活动
3. 可数名词：【尤作复数】所做的事情，活动，工作，消遣 词形变化
- 复数 activities
- an organic process that takes place in the body
- a process existing in or produced by nature (rather than by the intent of human beings)
- the state of being active
- (chemistry) the capacity of a substance to take part in a chemical reaction
- any specific behavior
- the trait of being active; moving or acting rapidly and energetically
radioactivity的中文意思