某同学做“利用单摆测定重力加速度”实验时，操作上错误或不合理的有 [ ]

A．取单摆的最大偏角大于5°

B．摆球摆动到最高点时开始计时

C．防止摆球在水平面内做圆周运动或椭圆运动

D．测出的摆线长就是摆长

E．在平衡位置启动停表，并开始计数，当摆球第30次经过平衡位置时制动停表，若读数为t，则T=

Mr. Black comes from America, and he has studied Chinese in China for five years. So you can talk with him _________.[ ]

A. either in English or in Chinese

B. not in Chinese but in English

C. just in English not in Chinese

D. neither in Chinese nor in English