回火保险器（）应有足够的强度能够承受燃烧混合气的爆炸压力。
A、防爆膜
B、外壳
C、过滤网
D、弹簧
参考答案：B
The doctor asked the patient to lie down _____ and breathe deeply. [ ]
A. flat
B. flatly
C. to be flat
D. to be flatly
They _____ in love for several years and then they_____ in 2008. [ ]
A. had been; got married
B. had fallen; married
C. fell; were married
D. were; married with each other
