青少年正在损害自己的健康，因为他们玩的电脑游戏太多了。

　　[即时训练2]

　　完成句子

　　This song sounds very pleasant. Let's go upstairs and see who _is_ singing(谁在唱歌)．

　　②She is_ always_ thinking_ of(总是想着) how she can do more for the people.

　　③The plane is_ taking _off(就要起飞了)．Please fasten your seat belt.

　　三、现在完成时

　　1．表示动作发生在过去，但对现在造成一定的影响或结果，常与already，yet，recently，never，before，so far，up to now等连用。

　　I have already made a plan for my study ahead of time.

　　我已经提前制定了学习计划。

　　2．表示动作从过去某一刻开始一直持续到现在，并有可能继续持续下去，常与表示一段时间的状语连用。

　　She left school three years ago and has worked as a teacher ever since.

　　她三年前毕业，从那时起一直当老师。

　　3．在"This/It is the first/second....last time＋that从句"与"This/It is the ＋序数词"或"形容词最高级＋名词＋that从句"中，从句中的谓语动词要用现在完成时。

　　This is the first time that I have been here.

　　这是我第一次来这里。

　　4．在时间或条件状语从句中，现在完成时可代替将来。

　　I won't believe it until I have seen it with my own eyes.

　　直到我亲眼见到才相信。

　　[即时训练3]

　　完成句子

Great_ changes _have _taken _place(发生了很大变化) in China in the past five years.

②It's the _best _film_ I_ have _ever_ seen(我看过的最好的影片)．It's worth seeing a second time.