情态动词must/should谈规则 — 英语填空题
题目
用 must, mustn't 或 should 填空（每词限用一次）。(1) This is a rule: You ___ wear a helmet when you ride a bike. (2) This is also a rule: You ___ swim in the river alone. (3) He looks tired after doing sports. He ___ drink some water and have a rest.