present simple 一般现在时
应用场景：
1）facts and truth
2) habits & things we do regularly
3) permarnent situation
present continuous 现在进行时
应用场景：
1）things that are happening at the time we are speaking
2) temporary situation
3) activities that are in progress
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BBC-Present Simple and Present Continuous
原文：http://www.cnblogs.com/shirley-ict/p/5526445.html