开关箱与所控制的设备距离不应大于（ ）米。
参考答案：C
如果三棱锥的三个侧面两两垂直，它们的面积分别为6 cm2、4 cm2、3 cm2，那么它的外接球体积是 ______cm3．
Some of students go _______ a parent's car to school every day. [ ]
A. in
B. by
C. at
D. on
