While talking to an uneducated person, we should use

The correct answer is B) his vocabulary. The governing idea is receiver-oriented communication: a message succeeds only when the listener decodes it, so the speaker must adapt to the listener's frame of reference. Using the words the listener already knows does this better than any general instruction to be simple or polite.

• A) Ordinary speech: Vague. Everyday speech may still carry jargon or abstractions the listener does not know.
• C) Simple words: Partly right, since simplicity helps, but it is a general rule. The examiner's key targets the more precise principle of matching the listener's own vocabulary, including familiar local expressions.
• D) Polite language: Courtesy is always expected, but it does not address comprehension, which is what the question tests.

This sits in the GS-IV ethics and communication syllabus, where audience adaptation is a basic principle of effective communication. It also links to civil-service outreach and grievance redressal, where officers must speak in the language people actually use.

Trap: Choosing C because "simple words" sounds like the obvious answer. The question asks for the principle, which is adapting to the listener's own vocabulary.