这个讲起来有点麻烦了。主句是一般现在时，从句什么时态都行eg: He says that he is reading a book now. 主句是一般过去时，从句用过去范畴的时态eg：He said that he would work hardeg:They said the had been to France这两个我举的例子从句一个用的过去将来时。一个用的过去完成时。主句一般过去时，但是从句是客观的真理，或者自然现象，还是一般现在时这个要注意，给你举个例子eg：The students asked me if the earth goes round the sun.这是客观真理。也是自然现象。这里的从句说的是地球围绕太阳转，这是永恒的真理，也是自然的现象，所以是一般现在时。其他的主句和从句中间的时态关系须看具体情况。还是给你举几个例子eg: My mother told me the cat had been fed by him.eg：She said that she had taken it home with her.另外宾语从句的从句部分是要遵循陈述的语序的。从句的结构：主+谓+其他[引导词]从句是陈述的语气 用that一般疑问 用if特殊疑问 用他专属的特殊疑问词eg：I‘m afraid that you are right这个理解起来应该比较简单，有疑问可以再站内信或者HI我
追问我是问I don't know that you study English这句话为什么用宾语从句？