In China phone talk is expensive. If you want to make it cheaper, make phone calls using t

But changing your DDD(domestic direct dial) and your IDD(international direct dial) calls for the net version, called voice over the internet protocol(互联网协议) or VOIP, requires you to choose between different types of technology, with different advantages.

If a telephone connection was a road, a regular phone call allows you and the person you are calling to share the road without anyone else. On this empty road, the connection is fast, efficient, and uninterrupted. But with VOIP technology, your voice is broken into millions of separated packets of information that share the road with all the billions of other bits of information on the Internet. When the packets reach the person you are calling, they are gathered to resemble your voice. Depending on which type of VOIP you are using, the speed of the Internet connection, Internet traffic, and the service provider, the resulting voice quality can vary—from quite good to quite awful.

The three main ways of using the internet to make calls are PC-to-PC(家用电脑) calls, PC-to-Phone calls and China's popular IP phone card.

VOIP calls are cheapest when they are made between two computers or between a PC and a telephone. For both, make sure you have a computer, an internet connection, a sound card, and most importantly, a headset(套头耳机) with a microphone.

People prefer IP phone calls to ordinary ones because the former is ______.

A．much more convenient

B．much cheaper

C．more dependable

D．more efficient