Known for his resilience and determination, (A)/ the runner refused to let a few (B)/ loses stop him then (C)/competing in future races (D).
Read the sentence to find out whether there is any grammatical or idiomatic error in it. The error, if any, will be in one part of the sentence. The corresponding letter of that part is the answer. If the given sentence is correct as it is, then choose option ‘No error’ as the answer response. (Ignore errors of punctuation, if any).

The correct option/answer is C.

Let us analyze the sentence step-by-step to identify the grammatical errors:

Part (A): "Known for his resilience and determination,"
This introductory participle clause is grammatically correct and correctly modifies the subject "the runner".

Part (B): "the runner refused to let a few"
This part functions correctly as the subject and main clause predicate up to the determiner "a few".

Part (C): "loses stop him then"
There are two distinct errors in this section:
1. Vocabulary/Spelling Error: The word "loses" is a verb (present tense, third-person singular of "lose"). However, after the phrase "a few", a plural noun is required. The correct noun form is "losses".
2. Conjunction Error: The adverb "then" indicates time or sequence. In this context, a temporal conjunction introducing a clause is needed, so "when" should be used instead of "then".

Part (D): "competing in future races"
This part completes the subordinate clause following the conjunction.

Thus, part (C) contains the grammatical errors ("loses" should be "losses", and "then" should be "when"). Therefore, part C is the correct answer.