Does anyone know which on it is?

Well first you should know that the ONLY ones you can use in ANY case are (SSS, ASA, AAS, and SAS) any other answer would be automatically invalid.

Then the S means Side, and the A means angles.

When you look at the diagram the lines you see in the triangles those are sides that are congruent.

Therefore, a Side, an Angle, and then another Side.

SAS

I'm sure the answer is a

Here, feel free to ask if there are any questions