[zh]Fix typo.

In [zh] Chapter 7.

1. Chinese left quote mark to English quote mark (4 times)
2. Chinese right quote mark to English quote mark (4 times)

Liam
Merge pull request #716 from LiamHuang0205/bugfix-typo

[zh]Fix typo.
[zh] Translate Chapter 7
[zh] Translate some paragraphs in Chapter 7.
Merge pull request #719 from lijunle/Chapter7

[zh] Translate some paragraphs in chapter 7