The correct answer is:
SAS.
Step-by-step explanation:
SAS stands for "side-angle-side." It states that if two sides and the included angle of one triangle are congruent to the corresponding two sides and included angle of another triangle, then the triangles are congruent.
In these triangles, sides AB and AC are marked congruent.
Side AR is congruent to itself by the reflexive property; this gives us our two sides.
∠BAR is marked congruent to ∠CAR. These angles lie between the two sides that have already been marked congruent. This gives us two sides and the included angle, so SAS.