流速计法测定水的流速时，为减少测量误差，当水深小于40cm时，采用一点法，水深大于40cm时，采用两点法。
参考答案：对
电压表是测量电路中两点间______的仪表，电压表在电路图中的符号是______．
In today’s fast changing and competitive world, to be able to learn faster and more effectively is not merely desirable; it is ________.
A．essential
B．worthwhile
C．challenging
D．sufficient
