按要求做题。

1. She has been swimming for 2 hours. (改为同义句)

She has been swimming       2 hour____.

2. My little sister is always behind me. (改为同义句)

My little sister       me                                 .

3. Tom played football for an hour. (改为现在完成进行时)

Tom                           football for an hour.

在生产、销售的食品中掺入有毒、有害的非食品原料的，即构成犯罪。