ASA is an acronym that stands for Angle Side Angle, meaning that in order to prove congruence you need to have those 3 congruences in a row within a triangle. We already know that Angle B and Angle E are congruent to each other, as well as Angle C and Angle F, so we need to know that the side in between the two angles are congruent, since the S is in between the two A’s. Therefore, we need to know that BC is congruent to EF, or answer choice B.
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