在超声波探伤中，为使声束在介质Ⅱ中聚焦，把聚焦探头的透镜（透镜材料为1）制成凹面的条件是介质Ⅰ的声速（）介质Ⅱ的声速。
参考答案：大
John admitted ________ the window and promised to compensate for it
A break B to break C breaking D to breaking
The weather in London is so changeable that people always take their umbrellas with them _____ rain.
A．in case of
B．in need of
C．in spite of
D．in favor of
