Final answer:
The sentence should be changed to option C: Robert Louis Stevenson started traveling to improve his health and soon began writing novels that would leave its impression on millions of readers.
Step-by-step explanation:
The sentence should be changed to option C: Robert Louis Stevenson started traveling to improve his health and soon began writing novels that would leave its impression on millions of readers. In the original sentence, there is a pronoun-antecedent disagreement. 'Robert Louis Stevenson' is a singular subject and should be followed by 'his' (singular possessive) and 'its' (singular possessive) to refer to 'novels', which is a singular noun.
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