题目内容：
根据以下内容回答题： Until recently the opportunities for criminal activities on the Internet have been low. However， the volume of business done on the Internet is growing rapidly， as people order books and other products and make money transactions. All this is creating temptations for hackers（黑客）。
Hackers are often young people who are interested in computers. They use them to move quietly to the Internet， looking for ways to break into computers systems run by banks， telephone companies and even Government departments. They look for examples of credit cards and try to steal the numbers.
Hackers rarely admit to a successful break-in. The first indication of a hacking may be when a customer discovers a wrong money transaction on a credit card account. It is harder to check on somebody misusing an online connection unless there is a massive download of information which would call the attention of the consumer.
The main idea of the first paragraph is that ______. A．the opportunities for criminal activities on the Internet have been low
B．the opportunities for criminal activities on the Internet are low
C．there are more opportunities for criminal activities on the Internet
D．people should not make money transactions on the Internet
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