To be symmetric with respect to the line showed, each point from both sides must be equally spaced from the line.
If we look, for instance, to the top of the figure, we see that it starts with a 1 unit horizontal line, which eliminates alternative A, because it starts differently.
Next, we have a 2-diagonal line going away from the middle line. This eliminates alternative C, becase it goes 3 units away, and D, because it goes only 1 unit down.
For this and for the other point in the figure, we get that the right alternative is B.