I don't know what to try next这个为什么不用which to try或者别的.要用what呢

如果要用which to try的话,上文一般会给出几个选择,比如说,i have a blue T-shirt and a yellow one, i don't know which to try next
如果没有明确的给出选择的话,一般是用what上文是there are lots of different kinds of food here。l don't know w____to try.是不是有语法在上面，不可以用which to try这里没有具体的什么选择，所以用what，which只能是在明确有选项的时候才可以用