直流系统一点接地时不会引起跳闸。
参考答案:对
Pleasant music is often played classes to make students refreshed and relaxed for a while.
A.between
B.among
C.over
D.after
如图所示,水平地面上有一个坑,其竖直截面为半圆。ab为沿水平方向的直径。若在a点以初速度v0沿ab方向抛出一小球,小球会击中坑壁上的c点。已知c点与水平地面的距离为圆半径的一半,求圆的半径。