在有线电视系统中，天线的主要任务是什么？
参考答案：
其任务是把空中的开路电视信号或卫星电视信号接收下来，送往系统中进行处理、传输和分配。
—Dad, could you buy me a computer like this?
—Of course, we can buy_________one than this, but_________it.
A．a better, better than
B．a popular, as good as
C．a more popular, not as good as
D．a cheaper, as good as
二氧化硫（SO2）是空气污染物之一．SO2中S元素的化合价为（ ）
A．0
B．+2
C．+4
D．+6
