be supposed to do 和be supposed to be doing 有什么区别?
be supposed to do 和be supposed to be doing 的区别在于动词不定式的形式不同。
具体分析：
1. be supposed to do ：应该干……；被要求干什么；理应做某事；应该。
to do是动词不定式的一般式，表示一般的情况，不强调具体的时间。动词不定式通常作为主语补足语。
举例说明：
I am supposed to pick up a packet .
我应该拿一个包裹。
I am supposed to help them.
我应该辅佐他们。
"He is supposed to come at one," replied his friend.
“他应该一点钟来。”他的朋友回答说。
Theoretically, the price is supposed to be marked on the shelf.
从理论上说，价格是要标在货架上的。
2. be supposed to be doing： 应该正在做什么事情；理应做什么。
to be doing动词不定式的进行时，强调动作正在发生或者进行着。
举例说明：
It means that your provider's platform is doing what it's supposed to be doing. （表达正在进行的事情）
它还意味着提供商的平台只做应该做的事情。
Kate is watching TV when she is supposed to be sleeping.（应该和看电视的时间同时）
凯特本该在睡觉的时候却在看电视。
People look the other way - even people who are supposed to be working for the subway . （表示现行阶段正在工作）
人们期待其它的方法，甚至被以为在地铁工作的人。
be supposed to be doing=按理应该正在……
例如：
You are supposed to do as you are told.按理你应该按照我要你做的去做.
You are supposed to be doing your homework now.按理你现在应该在做作业了.
类似的情况还有：
He happened to pass by the school gate.他碰巧要经过学校大门.
He happened to have read the book.他碰巧读过了这本书.
He happened to be reading the book.他碰巧正在读这本书.
如果你能看懂,请给我一个好评.
Be supposed to do something 本应该做某事 ; 应该 ; 应该做某事
