在英语作文中表述原因，可以采用以下几种常用句型：
直接陈述原因
There are three reasons for this.
The reason for this is obvious.
The reason for this is not far to seek.
The reason for this is that...
使用“as follows”引出原因列表
The reasons for this are as follows.
结合“it seems to me”表达个人观点
It seems to me that something is not valued highly enough... the possible reason may be...
使用“but possibly”强调态度或机构的影响
But possibly the problem lies not so much in （our institutions） as in （our attitudes）.
列举多个原因时使用“first, second, third...”等序数词
There are many factors that may account for this result, but the following are the most typical ones. First, …
结合具体情境使用
例如，在讨论老龄化现象时，可以这样表述原因：The Family Plan has been adopted for several years, most of the young generation are only child because their parents follow the government’s 。
在表达观点时，使用“additionally, in addition, again, also, and, besides, even more, furthermore, moreover, what's more, next”等词
例如：Nowadays, there are more and more XX in some big cities. It is estimated that. Why have there been so many XX？ Maybe the reasons can be listed as follows. The first one is 。
通过这些句型和表达方式，可以清晰、有条理地在英语作文中表述原因。根据具体的写作内容和语境选择合适的表达方法，可以使文章更具说服力和逻辑性。