I thought the kitchen window must ____(be) opened,(用括号词的适当形式填空）

I thought the kitchen window must ____(be) opened,(用括号词的适当形式填空）
I thought the kitchen window must ____(be) opened,(用括号词的适当形式填空）

I thought the kitchen window must ____(be) opened,(用括号词的适当形式填空）
must have done 结构
表示对过去的肯定推测,橱窗一定被打开过

be 因为must后面都用原型be

be.

I thought the kitchen window must have been opened.

be

have been别人的都错了，我是新加坡的