关键在于suppose的用法.
1.suppose sb to do sth.及其被动语态 be supposed to do sth.
2.suppose sb be doing sth及其被动语态 be supposed to be doing
不存在be supposed 后面直接加doing的用法,因为不符合被动语态语法.
例句：No one was supposed to tee us laughing.此处的laughing 是动名词用法,而不是所谓的be supposed doing .