Answer:
ABG
Explanation:
Triangles are labelled by stating all of its vertices, usually capital letters. Triangle FGA is made of the vertices called F, G and A.
For two triangles to be congruent, they must have all equal angles and equal sides. Although, you don't need to have all sides and angles information to determine if they are congruent.
Out of the three other triangles, triangle ABG has letters G and A in common with FGA. From this, we assume they both have at least two angles ( G and A ) and one side (GA) that are the same.
Therefore they might have ASA (angle side angle) similarity, which is one of the ways to tell if two triangles are congruent.
Three of the six pieces of information for angle or side are usually enough to determine if triangles are congruent (But not AAA similarity).