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根据短文内容， 从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。If your Internet or cable bill is more than you can afford — or suddenly looks higher than yousigned up for — you're hardly alone.Many American Internetand cable TV companies employ a shell game of limited-timepromotions and hidden, variable service fees to get us to pay more over time. Here are some tricks I learned from Internet service providers and consumer advocates. Check the website Broadband Now to find all the available service providers specific to your Zip 如图3-3-16所示，从AO输入的信号中，有直流电流和交变电流.问： (1)现要求信号到达BO两端没有直流电压，需要AB间接一个什么元件?该元件的作用是什么?(2)若要求信号到达BO端只有直流电压，而没有交变电压，则应在AB间接入一个什么元件? 该元件的作用是什么?图3-3-16