改错。

     Swimming is very popular in summer.

People like swimming in summer because of                                       1.__________

water makes people feeling cool. If you                                              2.__________

like swimming and swim in a wrong place,

it may not be safely. These years, more than                                       3.__________

nine hundreds children died while they were                                        4.__________

having a good time in the water most of                                              5.__________

them were students.

所谓基孔制，就是基本偏差为一定的孔的公差带与不同基本偏差的轴的公差带形成的各种配合的一种制度。