现在船用制冷剂以R22代替R12作制冷剂的主要理由是()。
A.不引起“温室效应”
B.不会产生“冰塞”
C.压缩机不发生“奔油”
D.对大气臭氧层破坏作用轻微
参考答案:D
Only when they were told the date of the wedding ________ their daughter would get married. [ ]
A. realized they
B. did they realized
C. did they realize
D. they did realize
在眼球壁中,无血管分布的是()
A、角膜
B、纤维膜
C、脉络膜
D、视网膜