硬盘的盘片上由一组（）组成；光盘的盘片上由一条从中心开始的（）组成，它又被称为轨道。
参考答案：同心圆；渐开线
---- busy schoolwork , the children also have to take arts , music and sports classes in their free time .
---- I wonder what they will become .
A．Rather than
B．Owing to
C．Except for
D．Apart from
绝缘油用于变压器、电压互感器、电流互感器上。（）
