为什么通风机要有集流器？
参考答案：
通风机配有集流器可使气流得到加速，在压力损失很小的情况下与整流罩配合，保证进气速度均匀，避免产生冲击和涡流。
When climbing the hill John was knocked unconscious by an _____ rolling stone. [ ]
A. untouched
B. unexpected
C. unfamiliar
D. unbelievable
— ____ of dumplings would you like?
— Beef and onion. [ ]
A. What color
B. What
C. What size
D. What kind
