Answer:
ΔBGC is right because Line E G is perpendicular-to CC'
Explanation:
The midpoints of the segments joining a triangle vertex with its reflected image will lie on the line of reflection. The segment will be perpendicular to the line of reflection.
In this scenario, a triangle will be right if it has a leg that is part of the segment joining reflected points, and a leg on the line of reflection. ΔBGC is such a triangle.
ΔBGC is right
_____
Comment on the problem statement
Point D came out of nowhere. A diagram would be most helpful.