Choose the correct one-word substitution for:
"A speech delivered without preparation"

Correct option is D

The correct one-word for the given group of words is (d) Impromptu.
Explanation : Impromptu means done or spoken without prior preparation, on the spur of the moment; an extemporaneous speech/act. (Hindi: आकस्मिक/बिना तैयारी के). Public speaking contexts often label such addresses as impromptu speeches.
Example: She delivered an impromptu vote of thanks when the host didn’t arrive on time.
Meanings of the given other options:
· Soliloquy: A speech in a play where a character speaks to themselves, revealing inner thoughts (Hindi: स्वगत भाषण).
· Rebuttal: A refutation; counter-argument to disprove a claim (Hindi: खंडन/खंडन-तर्क).
· Monologue: A long speech by one person (on stage or otherwise), not necessarily unprepared (Hindi: एकालाप).