Geometry

Question Analysis:
This question involves evaluating the validity of a syllogism.
The main focus is on determining whether the conclusion logically follows from the premises.

Key Concept Explanation:
A syllogism connects two premises to form a conclusion.
Here, the premises relate rhombuses and parallelograms.

Step-by-Step Solution:
Premise 1 states that all rhombuses are parallelograms.
Premise 2 states that all parallelograms have opposite sides equal.
Combining these, we conclude that all rhombuses have opposite sides equal.
The conclusion is valid.