个人觉得这个应该是属于客观真理,自然现象吧。若是客观真理还是用一般过去时态。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...