The image of ΔABC after a reflection across Line E G is ΔA'B'C'. 2 triangles are shown. Line E G is the line of reflection. Line segment D D prime has a midpoint at point F. Line segment C C prime has a midpoint at point G. Points B and B prime share a point.

Which triangle must be a right triangle and why?
ΔA'B'C' is right because it is the image of ΔABC.
ΔADC is right because AA' intersects AC at A.
ΔBCC' is right because B lies in the line of reflection.
ΔBGC is right because Line E G is perpendicular-to CC'.