Definition: If something is compulsory, you must do it because of a rule or law. Level: B2
法律规定在汽车上必须系安全带。
Wearing seat belts in cars is ___compulsory by law.
在我学校，游泳是必修的。
Swimming was ___compulsory at my school.
穿着传统服装不是强制的，但鼓励这样做。
Wearing traditional dress is not ___compulsory, but it's encouraged.
