SAT inequality problem I've been studying from Collegeboard SAT practice tests, and I've stumbled with a inequality problem, which I can't seem to understand even with SAT answer explanation.I would greatly appreciate it if anyone could help me.
$$ y ≤ 3x+1 $$
$$x-y > 1 $$
Which of the following ordered pairs (x, y)  satisfies
the system of inequalities above?
$$A) (−2, −1) $$
$$B) (−1, 3 )$$ 
$$C) (1, 5 )$$ 
$$D) (2,-1)$$
edit
This is the answer explanation they give me: 
Choice D is correct. Any point (x, y) that is a solution to the given system of inequalities must
satisfy both inequalities in the system. Since the second inequality in the system can be
rewritten as $$y < x − 1$$, the system is equivalent to the following system.
$$ y ≤ 3x+1 $$
$$x-y > 1 $$
Since $$3x + 1 > x − 1$$ for $$x > −1 $$and$$ 3x + 1 ≤ x − 1$$ for$$ x ≤ −1$$, it follows that $$y < x − 1$$ for $$x > −1$$ and $$y
≤ 3x + 1$$ for$$ x ≤ −1$$. Of the given choices, only (2, −1) satisfies these conditions because $$ −1 < 2 − 1 = 1. $$

$$y\leq3x+1$$ $$x-y>1\implies y<x-1$$
You can solve this graphically

The region which solves these inequalities is the region below the two lines. By plotting the 4 points, you'll see option D is the only one which lies in the region.
