营业线改建桥涵工程不包括内容()?
A.桥梁墩台加高与落低
B.增加桥梁孔数
C.涵洞接长
D.填塞桥孔
参考答案:C
如图所示把正在发声的闹钟放在玻璃罩内,闹钟和罩的底座之间垫上柔软的泡沫塑料,逐渐抽出罩内的空气,闹钟的声音会逐渐变小,直至听不到声音.这个实验说明了( )
A.声音是由物体振动产生的
B.声音必须通过介质才能传播
C.声波在玻璃罩中发生了反射
D.声波在传播过程中能量逐渐减少
There are many places in the world ________ have been visited only by a few, many ________ are
of an enormous beauty.[ ]
A. where; of which
B. which; of whom
C. that; of which
D. that; of whom