The altitude of a triangle is defined as a segment connecting one of the vertex of the triangle with the opposite side of the triangle (or with an external prolongation of it), forming a right angle with it.
Note that the altitude of a triangle can also be outside the area of the triangle.
If we look at the picture, we see that:
- IH is a side, so it is not an altitude of the triangle
- KH is an altitude of the triangle, since it connects the vertex H with the external prolongation of IG, and it makes a right angle with it
- GJ: we don't know if it is an altitude, since we don't know if it forms a right angle or not
- GH: it is a side of the triangle, so it is not an altitude
Y=-2 is a horizontal line, each point which lies on this line has the y-coordinate -2. Only in option C both points have the y-coordinate equal to -2. The answer is C.