Traditional folk arts of Tianjin like paper cutting ________ at the culture show of the 2010 Shanghai

World Expo.[ ]

A. are exhibiting  

B. is exhibiting

C. are being exhibited  

D. is being exhibited

一列横波沿x轴正向传播，a、b、c、d为介质中沿波传播方向上四个质点的平衡位置。某时刻的波形如图（a）所示，此后，若经过3/4周期开始计时，则图（b）描述的是

A．a处质点的振动图象

B．b处质点的振动图象

C．c处质点的振动图象

D．d处质点的振动图象