Because donate blood have several advantages---have应改为has.后面也有个要改.这是篇提纲式作文,其写作模板：
1． 对立观点式
A．有人认为X 是好事,赞成X, 为什么?
B． 有人认为X 是坏事, 反对X,为什么?
C．我的看法.
Some people are in favor of the idea of doing X. They point out the fact that 支持X 的第一个原因.They also argue that 支持X 的另一个原因.
However, other people stand on a different ground. They consider it harmful to do X. They firmly point out that 反对X 的第一个理由. An example can give the details of this argument: 一个例子.
There is some truth in both arguments. But I think ……
其实我以前写这种文章也是三段式,跟你一样,第一段：引语.第二段：简述两方观点及原因,第三段,自己的观点.也得高分了呀,亲的文笔还是挺好的,可能是你老师思路不一样,建议找他询问询问--上学吧为你回答.