电路中元器件较多时，表示两点间的电压较繁琐，用电位表示，则简单清晰。
参考答案：对
People always interrupted his before he________what he was trying to day.
A．finishes
B．would finish
C．had finished
D．has finished
已知三角形ABC，其三边BC、CA、AB的长度分别为a、b和c，，则夹角∠BAC的cos值为（）。
A.
B.
C.
D.
