It is uncertain __side effect the medicine will bring about,although about two thousand patients

问题描述:

It is uncertain __side effect the medicine will bring about,although about two thousand patients
have taken it .这道题答案是WHAT,我想问为什么不能用WHETHER ,求详解

如果是用whether,句子就必须改写了:
It is uncertain WHETHER the medicine will bring about ANY side effect.