Answer:
See below.
Explanation:
I had to look this up myself, but now I can explain it to you. There are better sources on the web, but it comes down to this:
See the open circles at 1 and -1? That means it's an open interval that doesn't include the end points. And when you have that, the standard notation is parentheses.
If those circles were solid (colored in), then it would be a closed interval that does include the end points. And the standard notation for that is closed brackets.
One side could be closed, and the other open, or both closed, and that's why you have those other combinations of brackets and parens as answer choices.
Weird, but there ya go. Hope it helps, but search on Interval Notation for more. Be good.