Correct option is C
The correct substitution of the highlighted words is (c)
No substitution.
Explanation:
· The sentence is in present tense, talking about a general fact/belief held by some people currently.
· “Who believe” is grammatically and contextually correct.
· “That the earth is flat” is the object clause of the verb "believe".
Grammatical Rule Used:
Use
simple present to state
general truths or ongoing beliefs. The relative pronoun “who” refers to “people”, and “believe” matches subject-verb agreement.
Example:
· There are scientists who claim that aliens exist.
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Information
Booster: Use "believe" (verb) not "belief" (noun) after "who" because we need an action here, not an object.