In order to make a quotation clearer or fit grammatically into your sentence, you can add words and phrases enclosed by
a. ellipses.
b. parentheses.
c. commas.
d. brackets.

The correct answer is letter d which is brackets. When writers put or alter words in a direct quotation, they use square brackets. These are placed around the change. The brackets always go together in pairs. Enclose words are intended to clarify meaning, provide a brief explanation, or to help integrate the quote into the writer’s sentence.  A common error of writers is to make use of the parentheses in place of brackets.

We should feel gravity around us. if it ever ends what will life be like. the reader will definitely have alot of questions towards gravity being ended