compulsory

adj. /kəmˈpʌlsəri/ B2

强制的；必修的

Must be done because of a rule or law; mandatory.

仙境例句

Washing was only an extra, but sums were compulsory: every young turtle had to learn them.

洗衣服只是附加课，可算术是必修课，每只小海龟都得学。