Q:

When to use 별로 vs 그리?

In the following sentences (from duolingo):

그것은 그리 안 좋아요.

I used 별로 instead of 그리 and got wrong. 
But I'm not sure what is the difference between them and when I should use one over the other. Both seem to mean the same thing (at least from my dictionary). 
So when should I use 그리 over the 별로 and vice versa?

A:

It's almost the same meaning if the sentence is not a question.
In my case, I would rather use 그리 안좋아요 when the thing is expected to be good but disappoints me actually.
The difference stands out if you're going to use it with questions:
결혼하면 뭐가 그리 안좋아요?
In a situation where you thought the marriage is not so bad, but someone told you it isn't good, you may ask with this sentence:

결혼하면 뭐가 별로 안좋아요?
You already know the marriage is bad and you're asking what is so bad exactly?.

