【题目】Only if a teacher gives permission ________.
A.a student did allow to enter the room
B.is a student allowed to enter the room
C.did a student allow to enter the room
D.a student is allowed to enter the room

【答案】B
【解析】only if引导的状语从句放在句首时，主句用部分倒装。be allowed to do被允许做……。句意：只有得到老师的许可，学生才允许进入房间。根据句意，故选B。