假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌的以下作文。文中共有10处语言错误，每句中最多有两处，每处错误仅涉及一个单词的增加，删除或修改。

增加： 在缺词处加一个漏字符号（^）,并在其下面写出该加的词;

删除：把多余的词用斜线（\）划掉;

修改： 在错词下划一横线，并在该词下面写出修改后的词。

注意：1).每处错误及其修改均仅限一次；

2). 只允许修改10处，多者（从第11处起）不计分。

    It is good to see that today more people have realized the importance exercising and are playing sports regular. But the problem is that there are not enough sports facilities to meet the public growing demand. I love playing basketball and often play with my friends on weekends. Therefore, it is difficult to rent a basketball field and possible to find a free one. It seems that all courts in the city were always full. Weather permitted, we can play in outdoors. But on rainy days or in winter we have to turn to indoor courts. There are not much in my city, and the charge is high. The government should build more public sports facilities, so easier access will encourage more people participate in sports.

—Good idea!

“龙生龙，凤生凤，老鼠的儿子会打洞”这句谚语揭示的生物现象是（    ）