According to the weather report,it( rains)tomorrow.

According to the weather report,it( rains)tomorrow.
为什么不是will rain呢

你看看下面的内容：
介词according to 的用法说明
1.用于according to,意为“根据”,为复合介词,后接名词或代词.注意以下用法：
(1) 主要用来表示“根据”某学说、某书刊、某文件、某人所说等或表示“按照”某法律、某规定、某惯例、某情况等.如：
Everything went off according to plan.一切都按照计划实现了.
According to my watch it is five o’clock.照我的表,现在是5点钟.
Each man will be paid according to his ability.每个人将根据他的能力获得报酬.
(2) according to 表示“根据”,通常是指根据别人或别处,而不能根据自己,所以其后不能接表示第一人称的代词（如me,us）,同时也很少接表示第二人称的代词（you）,但用于第三人称（如 him,her,Jim,Mary,the doctor等）则属正常用法.如：
误：According to me,the film is wonderful.
正：In my opinion,the film is wonderful.依我看,这部电影很不错.
另外注意,according to后也不接view（看法）和opinion（意见）这类词表示看法的词.如：
误：According to my opinion,he did it very well.
正：In my opinion,he did it very well.在我看来,他干得很不错.
2.用于according as,意为“根据”“随……而定”,后接从句.如：
Everyone contributes according as he is able.每个人根据自己的能力做出贡献.
You will be praised or blamed according as your work is good or bad.根据你工作的好坏,你会得到表扬或批评.
但是,对于那些由what,which,whether,how,when,where等引导的句子,其前要用according to,不用according as.如：
He is an honest businessman,according to what everyone says.根据大家所说,他是位诚实的商人.
The amount of tax people pay varies according to where they live.居住地不同,人们所交的税额也各不相同.
These apples have been graded according to how big they are.这些苹果已经按照大小分了等级.
They were arranged according to when they happened.它们是按发生的时间安排的.