Answer: Sometimes. All we need to know is if one pair of sides are the same length between the triangles, and that is enough info to know if triangle ABC = triangle DEF. We don't have any such info, so we just say "sometimes" to account for this situation.
Answer: 60 degrees. Angle B = angle E, and we're told that B = 60, so E must be 60 as well for the two angles to be congruent.
Answer: Always. Equilateral triangles have the same angle measure (60 degrees each). Any two triangles with corresponding congruent angles are similar triangles.
