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 hard
eg: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
例子我也不多举了.