be supposed to do sth 应该做.为啥子 suppos.这个单词要变成加d 还有 tell us what happened 这个句子中“发生”要用ed呀?、 还有背词组有啥规律吗?

be supposed to do sth 应该做.为啥子 suppos.这个单词要变成加d 还有 tell us what happened 这个句子中“发生”要用ed呀?、 还有背词组有啥规律吗?
be supposed to do sth 应该做.为啥子 suppos.这个单词要变成加d 还有 tell us what happened 这个句子中“发生”要用ed呀?、 还有背词组有啥规律吗?

be supposed to do sth 应该做.为啥子 suppos.这个单词要变成加d 还有 tell us what happened 这个句子中“发生”要用ed呀?、 还有背词组有啥规律吗?
1.be supposed to 的用法
用法一：be supposed to...其中to是动词不定式符号,不是介词,其后要跟动词原形.当be supposed
to...的主语是“人” 时,意为“应该……
”；“被期望……”,它可以用来表示劝告、建议、义务、责任等,相当于情态动词should.如：
Everyone is supposed to wear a seat-belt in the car.
每个人在汽车里都应该系安全带.
Teachers are supposed to treat all the students alike.
老师应该对所有的学生一视同仁.
用法：当be supposed to...的主语是“物”时,它表示“本应；本该”,用于表示“某事本应该发生而没有发生”.如：
The new laws are supposed to prevent crime.这些新法令本应该起到防止犯罪的作用.
The train was supposed to arrive half an hour ago.火车本应在半小时之前到达.
用法三：be supposed to后面接“have + 过去分词”时,表示“本应该做某事而没做”.如：
You are supposed to have handed in your homework by now.
现在你应该已经把作业交上来了.
He is supposed to have arrived an hour ago.他应该一小时前就到了.
用法四：be supposed to...的否定结构为be not supposed
to...,它常用于口语中,意为“不被许可；不应当”.如：
She was not supposed to be angry about that.她本不该为那件事而生气的.
You are not supposed to smoke on the bus.你不应该在公共汽车上吸烟.
2.
tell us what happened 是 告诉我们发生了什么.既然是发生了,则就是过去式了,所以要加ed形式的过去式
英语除了记住单一的语法,还要根据语境去理解句子的意思和语句所要表达的内容,多读多看多听就会慢慢理解的

因为是被要求做，是被动语态，所以加ed
这个发生是以前就发生了的，是过去式
背词组就按音标来，很好记住的
ps：本人的话如有不对请原谅，基本就是这样了，只是措辞问题