在X≥3N的距离上,当声程不变,孔径增加1倍时,长横通孔的回波高度差为()。
A.3dB
B.6dB
C.9dB
D.12dB
参考答案:A
--- Why didn’t you tell me the news of the meeting?
--- I knew nothing about it, or I _______ you.
A.would tell
B.had told
C.told
D.would have told
结合协议性国际分工原理,分析实现经济一体化的条件。