Analogy — “Paper : Tree :: Glass : ?”. Select the option that best completes the ‘product : primary raw material’ relationship.

Introduction / Context:
Analogy questions test whether you can spot and replicate the exact relationship that holds between the first pair of words. In the stem, “Paper : Tree,” the first item (paper) is a product and the second item (tree/wood pulp) is the characteristic raw material used to make it. We must choose the material that stands to “glass” as “tree” stands to “paper,” i.e., the primary raw input for the product.

Given Data / Assumptions:

• Paper is conventionally produced from wood pulp derived from trees.
• Glass is conventionally produced from silica-rich sand, typically with additives like limestone and soda ash.
• Exactly one option should map “product → primary raw material,” not “product → use,” “product → place,” or “product → finished good.”

Concept / Approach:
The core idea is “finished product” versus “canonical raw material.” For paper, that material is wood pulp (tree). For glass, the textbook base is silica sand (SiO2), commonly called sand. Other listed terms may be related to glass but do not encode the same foundational “raw input” relationship by themselves.

Step-by-Step Solution:

Verification / Alternative check:
Real-world glass batches include sand, limestone (CaCO3), and soda ash (Na2CO3). However, “sand” is the fundamental base; limestone and soda ash are additives/fluxes to adjust melting point and durability. Therefore, “Sand” most faithfully mirrors “Tree.”

Why Other Options Are Wrong:

Common Pitfalls:
Confusing product applications (window, mirror) or secondary ingredients (soda ash) with the principal raw material.

Final Answer:
Sand