点击下方单词,选择对的这个单词
点击下面链接下载与本句相关的学习资源，包括PDF教材和音频练习，方便课后复习：
1. required by rule
e.g. in most schools physical education is compulsoryattendance is mandatoryrequired reading
Synonym: compulsorymandatory
2. necessary for relief or supply
e.g. provided them with all things needful
Synonym: neededneedfulrequisite
动词requireneedask
形容词electiveoptional
多通过句子记忆单词，而不是单独死记硬背。
