i am against building a factory为什么be动词后接介词?

i am against building a factory为什么be动词后接介词 i am against building a factory为什么be动词后接介词? 英语翻译I am writing to say that I am against building a new zoo should 后加介词against 时需加be 动词么,we should against it.这句话对么 英语中介词的问题!against不是有介词的用法吗?介词前面不是应该是名词或动词或形容词吗?那么I am against 为什么不能说i saw a ladder lean against the building 为什么leading a happy life前要加be动词?如：I am leading a happy life. be动词am算是介词吗? both或者neither出现时 比如neither he nor I am a doctor 为什么be动词用am 有 be going to 后可不可以接瞬间动词?即可不可以说I am going to die? i'm crazy about it 为什么加be动词"am"? 为什么 i work here.没be动词 而 i am working here 有be 动词 急