should和must都是情态动词，表达说话人的一种语气和态度。
should表示“应该”，语气委婉。
must有“一定”的意思，语气比较强硬。
Example: Visitors should inform the receptionist of their arrival. 来宾在到达时应当知会接待员。
Example: We should have bought a new lock for the front door. 我们本该买把新锁安在前门上。
Example: Linda’s ideal house must have a luxurious swimming pool. 琳达理想中的房子一定要有豪华的游泳池。
Example: Mrs. White told all the students that they must finish their homework before 6 p.m. today. 怀特女士告诉所有的学生，今天下午6 点之前务必完成作业。
