You stepped into the lab with your shoes on? You’re to take them off before you enter it.

问题补充：

You stepped into the lab with your shoes on? You’re to take them off before you enter it.

A. invited

B. supposed

C. forbidden

D. permitted

答案：

A. invited

(答案→)B. supposed

C. forbidden

D. permitted

解析：考查动词。be supposed to do应当做某事。根据句意你进实验室之前应当把鞋脱了，选B。