风险转移的常见方式是()。
A.保险
B.保证金
C.履约保函
D.欧标保证金
参考答案:A
The Natural Approach believes that the teaching of () should be delayed until comprehension skills are established.
A. listening
B. speaking
C. reading
D. writing
判断声源的距离主要依靠声压和主观经验,一般在自由空间中,距离每增加一倍,相应的声压级将减少( )dB。
A.1
B.5
C.6
D.10