单选题
It's simply amazing what a cell phone can do these days. Teenagers know this better than anyone. They'll tell you their super-thin phones are really pocket-sized entertainment systems. They can listen to music, watch music videos, and play computer games. They can take photos and send text messages to their friends. Businesspeople know this, too. For them, cell phones are really high-tech business tools. They can review business documents and read e-mail. They can check their appointment calendar and get directions to a client's office. So what features do cell phones have these days? That depends on the model, of course. But the standard features include a digital camera, MP3 player and PDA. Newer models also have video-recording capacity. Perhaps most importantly, some phones offer wireless (无线) Internet access. That means you can use your phone to read and send e-mail and browse the Web. You can download music, games and video files. You can even watch short "made-for-phone" dramas.
单选题
According to the passage, ______ know better the amazing functions of a cell phone than anyone.