单项选择题

Do your children lie to you and their friends about their activities online Do they feel empty, depressed and irritable when not at the computer Do they have problems with school or work, yet they always seem to feel energized again when they are at the computers surfing the internet If you answered "yes" to one or even more of the above questions, your children are suffering from internet addiction. The amount of time kids spend online is a source of headaches for many parents. At first, parents welcomed the Internet into their homes, believing they were opening up an exciting new world of educational opportunities for their children. But soon, to their disappointment, instead of using the Internet for homework or research, their kids were spending hours instant chatting with friends, playing online games or even talking to strangers in chat rooms, which is posing real dangers to the children.
Maintaining a healthy balance between entertainment media and other activities in children’s lives has always been a challenge for parents. The Internet has made this challenge even more difficult. The engaging nature of Internet communications and interactive games means many children and teens have trouble controlling the time they spent online.
Unfortunately, parents and teachers do not realize that there is a problem until it becomes serious. To make it worse, Internet addiction is not widely recognized by the medical community. (Mental health practitioners continue to debate whether this behavior is an "addiction," with some preferring to identify it as "behavior control problems.
Children and young people can easily become "hooked" on online activities such as multi-user games, instant messaging with their pals and chat rooms. The children most easily influenced, according to the Computer-Addiction Services at Harvard Medical School, are those who are "lonely and bored or from families where nobody is at home to relate to after school."
Children who are unpopular or shy with peers are often attracted to the opportunities for creating new identities in online communities. Boys, in particular, are frequent users of online role-playing games, where they have new identities and interact with other players. Although playing these games with thousands of other users may appear to be a social activity, for the troubled child or teen, too much playing can further separate them from friends and peers.

What is the "challenge" the author is talking about in paragraph 2（）

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