Analogy — Place containment/occurrence: Lightning : A :: B : sky

Introduction / Context:
We want entities naturally found “in” their environments. Lightning appears in/among clouds; a rainbow appears in the sky. Thus the mapping is “lightning : cloud :: rainbow : sky”.

Given Data / Assumptions:

• Lightning is observed in cloud formations.
• Rainbow is observed in the sky.

Concept / Approach:
Use “phenomenon : medium/location”.

Why Other Options Are Wrong:

• Rain/Thunder etc. mix causes and effects or reverse relations.
• “Sky : Rain” flips containment.

Final Answer:
A. Cloud, B. Rainbow