What of the following shows the polynomial below written in descending order 3x^3+9x^7-x+4x^12

Descending order is the traditional way that a polynomial is displayed, and is written where the degree is highest on the left, and lowest on the right.

So, from left to right, the degree decreases.

This polynomial written in decreasing order would look like this:

4x^12 + 9x^7 + 3x^3 - x

3x^3+9x^7-x+4x^{12}