Geometry

Question Analysis:
This problem requires knowledge of triangle congruence postulates.
The focus is on selecting the correct rule that guarantees the congruence of △RST and △XYZ.

Key Concept Explanation:
There are several ways to prove two triangles are congruent:
SSS (Side-Side-Side): All three sides are congruent.
SAS (Side-Angle-Side): Two sides and the included angle are congruent.
ASA (Angle-Side-Angle): Two angles and the included side are congruent.
AAS (Angle-Angle-Side): Two angles and a non-included side are congruent.

Step-by-Step Solution:
Given information:
RS ≅ XY (side)
ST ≅ YZ (side)
∠S ≅ ∠Y (angle between these sides)
The SAS postulate states that if two sides and the included angle of one triangle are congruent to two sides and the included angle of another triangle, the triangles are congruent.
Since ∠S is between RS and ST, the correct answer is B. SAS.

Option Analysis:
(A) SSS: Incorrect. We are given two sides and one angle, not three sides.
(B) SAS: Correct. Two s...