3300前置器需要在它的VT端和COM端之间提供（）直流电压。
A、-12V
B、-24V
C、+12V
D、+24V
参考答案：B
_______ jeans were invented over 100 years ago, they're still in fashion today.
A．Because
B．If
C．Although
D．Since
4G流量包不包含2G、3G流量，仅限4G流量。
