指针式万用表一般用于检测普通电器及其线路，对于电子控制系统的元件及其线路的检测需使用高阻抗的万用表。（）
参考答案：对
Helen is 15 years old, and Joan is 15, too. So Helen is ____ Joan. [ ]
A. as big as
B. as older as
C. as old as
D. so old as
空气冷却器的冷媒进口温度，和空气的出口干球温度相比应( )。
A．至少低5℃ B．最多低5℃ C．至少低3.5℃ D．最多低3.5℃
