Classification — container/part relations: select the pair that does NOT express an “in/on/part-of” relation.

Introduction / Context:
Three pairs show “in/on/part-of” relations (physical inclusion/attachment). One pair instead expresses a purpose/usage relation (a ticket is for a train), not inclusion/attachment.

Given Data / Assumptions:

• Stamp : Letter → affixed on a letter.
• Ink : Pen → ink is in a pen.
• Car : Engine → engine is in a car (part-of).
• Ticket : Train → for traveling by train; not contained in/on the train.

Concept / Approach:
Filter pairs by “physical inclusion/attachment.” The single purpose-only mapping is the odd pair.

Step-by-Step Solution:

Verification / Alternative check:
Ask “Is the right-hand item physically in/on the left?” Only B answers “no.”

Why Other Options Are Wrong:
They preserve inclusion/attachment.

Common Pitfalls:
Equating “related to” with “contained in/on.”

Final Answer:
Ticket : Train