Correct option is C
The correct substitution of the highlighted words is (c) No substitution required.
Explanation:
· The verb “refrain” is correctly followed by a “from + gerund” structure (“from speaking”) and expresses the act of holding oneself back from doing something, especially voluntarily.
· “Requested the audience to refrain from speaking” is perfectly grammatically and contextually correct.
Grammatical Rule Used:
· Refrain is an intransitive verb used with the preposition “from” followed by a gerund (verb+ing).
· Example: Please refrain from using your phone in the library.
Information Booster:
· Avoid using “restrain” in such cases as it implies physical force.
· "Restrict" requires an object and generally refers to external imposition of limits, not voluntary action.