有几道英语一般现在时的练习题

有几道英语一般现在时的练习题
五、 用所给词的适当形式填空.
1.I like collecting Chinese stamps.I usually ( collect) stamps.
2.We (go) to school from Monday to Friday.
3.My parents (like) (read) science magazines.
4.Tom usually (watch) TV after school,
he (like) (watch) TV.
5.She (want) to (go) to the park.
6.I usually go (swim) after school.
.I usually go (swim) after school.
为什么swim 要变为swimming？