The boy was supposed _____ at school but his mother found him playing in the park.
A.to be reading
B.reading
C.read
D.have read
请帮忙分析正确选项,并翻译整句话,非常感谢!
顺便问一下为什么要用was supposed ,是什么用法?
此句是否可以用to read?

The boy was supposed _____ at school but his mother found him playing in the park.
A.to be reading
B.reading
C.read
D.have read
选A, to be reading,这里是be supposed to do的固定用法，译为“应该是在做某事；被期望做某事”
整句翻译：这个男孩应该正在学校读书，但他的妈妈发现他正在公园玩。
从后半句“but his mother found him playing in the park”可以判断出本句的意思是想表达那个时刻正在做某事，所以用to be reading 要比to read更贴切。