It is [urgent/necessary/convenient/desirable/advisable] for sb. to do sth.
have [trouble/a difficult time] [in doing sth./with sth.]
举 例证：It can be given by a (well known/concrete) example that ____________. / In order to see this point clearly, let us to see an example:____________/To illustrate this, there is an example that is very persuasive:____________.
第一点原因：
The main/first reason is that ____________.
First, we can observe easily that in modern society, ...
In the first place
To begin with, (a good roommate should ____________)
第二点原因：
Besides, the further reason why I advocate AAA is that ____________.
[The second/another] reason for [my/people’s] propensity for A is that ____________
[The second/another] desirable quality for a good roommate is that ____________
第三点原因：
Moreover,____________
The third reason, [not the last/however], goes this way: ____________
写完三条原因还可以再写：Maybe there are some other reasons( to show____________). But
it is generally believed that the reasons mentioned above are commonly acceptable.
最后意犹未尽或者字数不够可以加这么一句：
Nevertheless I must admit that people can do well without AAA, but no one can ignore the additional convenience and satisfaction offered by AAA. Such experience will definitely be helpful in one’s later life.
