A:有力作用在物体上,物体一定发生形变,撤去此力形变完全消失
B:有力作用在物体上,物体不一定发生形变
C:力作用在硬物体上,物体不发生形变;力作用在软物体上,物体才发生形变
D:一切物体受外力作用都要发生形变,外力撤去,形变不一定完全消失
A,B两物体在同一直线上运动的v﹣t图象如图所示.已知在第3s末两物体相遇,则下列说法正确的是( )
“花下成千成百的蜜蜂嗡嗡地闹着”,这个“闹”字用得极妙,不禁使人想起古代诗人宋祁的一句诗:____。
Flags have existed for over 3,000 years. The earliest flags were wooden or metal poles with a carving. About 2,000 years ago pieces of fabric were added to some poles for decoration. Over the next 500 years the free-flying part of the flag became more important.
读“气温曲线和降水柱状图”,读“气温曲线和降水柱状图”,甲图气候类型的特点是( )