Functional association analogy: “Needle is related to Thread in the same way as Pen is related to …” — select the item that pairs functionally with a pen.

Introduction / Context:
A needle uses thread to perform its function (stitching). Analogously, a pen requires ink to write. The relationship emphasizes the essential material enabling the tool’s core function, not accessories or outputs.

Given Data / Assumptions:

• Needle ↔ Thread (enabling medium).
• Pen ↔ Ink (enabling medium for writing).

Concept / Approach:
Match “tool : essential medium.” Avoid confusing with “tool : accessory” (cap) or “tool : output” (word on paper).

Step-by-Step Solution:
1) Identify the enabling substance for a pen: ink.2) Select “Ink.”

Why Other Options Are Wrong:

• Cap: Accessory.
• Paper: Surface, not the writing medium inside the pen.
• Word: Output/concept, not a medium.
• Notebook: Substrate/collection of paper.

Common Pitfalls:
Confusing output or accessory with the enabling material.

Final Answer:
Ink