短波、超短波电磁场作用深度可达骨骼；而直流电、低中频电流作用主要在皮肤层，次为肌层。
参考答案：对
The boy's bad behavior _______ his mother many sleepless nights. [ ]
A. cost
B. made
C. cause
D. bring
太阳系的直径为150亿公里。( )
