数据通信速度最快、安全性最好、出错率最低的硬介质是( )。
A．光缆
B．无线电或微波
C．同轴电缆
D．双绞线
参考答案：A
解析： (略)
补全对话根据对话内容，在横线上填入适当的短语或句子，使对话完整、通顺。
A: I hear you won a million dollars in the lottery yesterday, 1
B: Yes, it is. I really did!
A: 2
B: I would help animals.
A: 3
B: Because I think helping animals is helping people.
A: 4
B: Pandas. I like pandas best. 5
A: I like all animals. Animals are our friends. I would help animals, too.
B: I'm very happy to hear that.
两个扇形的圆心角度数之比是2：3，半径之比是3：5，则它们的面积之比是______．
