题目内容：

关于4个英语句子的并列结构问题
1、A great many people are surfing on line within a stretching spider web,either to entertain themselves or to meet their work’s needs.
2、The spider web serves as a symbol of Internet,both connecting people and isolating them from each other.
第一个句子中,通过either...or...连接的是to的结构,而第二个句子中both...and...连接的是doing.它们两个为何不同?
因为either...or和both...and本身的区别还是所在句子的不同而引起的一个接to,一个接doing?
3、Once indulged in the fictitious world,people feel reluctant to approach others and to concentrate on real life.
4、It is necessary for us to use Internet in a reasonable way and restrain from overindulgences.
第三句中有个and引起的并列,前面是to approach,后面是to concentrate,因为并列,所以前后结构一致,这个我理解,呵呵.可是第四个句子中and前是to use,而and后是restrain,为何不是to restrain哩?