It's uncertain____side effect the medicine will bring about.,although about two thousand patients

问题描述:

It's uncertain____side effect the medicine will bring about.,although about two thousand patients
It's uncertain____side effect the medicine will bring about,although about two thousand patients have taken it
答案是what,
我想知道为什么不能用whether,

what充当从句中的宾语,可以把从句调整为the medicine will bring about what side effect .