In the following sentence improvement question, the underlined part is second to one: Usain Bolt is second to one as an athlete. Choose the best replacement, or select No improvement if the phrase is already correct.

Introduction / Context:
This sentence improvement question focuses on a very common English idiom: second to none. The sentence reads Usain Bolt is second to one as an athlete, with second to one underlined. The intention is to say that Usain Bolt is the best and that no other athlete is above him. The phrase second to one, however, suggests that one person is still ahead of him, which contradicts this idea. You must choose the idiom that correctly expresses that no one is better than Usain Bolt as an athlete.

Given Data / Assumptions:

• Sentence: Usain Bolt is second to one as an athlete.
• Underlined phrase: second to one.
• Options: second to no one, second to none, none of second, No improvement, second to everyone.
• Intended meaning: Usain Bolt is the best; nobody is superior to him in athletics.

Concept / Approach:
The fixed idiom in English for expressing that something or someone is the best is second to none. It literally means that there is no one to whom the person or thing is second in rank. Second to one would mean that there is exactly one person ahead, so the subject is in second place, which is not the intended praise. Second to no one is close in meaning but not the standard set phrase. Therefore, second to none is the most idiomatic and correct improvement to show Usain Bolt's unmatched excellence.

Step-by-Step Solution:

Verification / Alternative check:
Read the improved sentence: Usain Bolt is second to none as an athlete. This clearly means he is at the very top. In contrast, Usain Bolt is second to one as an athlete would be interpreted as he is only in second place, which is a much weaker compliment. Second to no one is understandable but less common than the compact, widely recognised idiom second to none. Exam questions almost always expect the standard idiom that appears in dictionaries and textbooks, so second to none is preferred.

Why Other Options Are Wrong:
Option A (second to no one) is close in sense but is not the classic idiom; exam-oriented English typically prefers second to none. Option C (none of second) is ungrammatical and meaningless. Option D (No improvement) is clearly wrong, because second to one expresses the opposite of what is intended. Option E (second to everyone) suggests he is below all other athletes, which is the exact opposite of the intended praise.

Common Pitfalls:
Students sometimes misremember idioms, especially when numbers are involved, and produce variations like second to no one or second than none. Exams are strict about such expressions and usually accept only the standard, established form. Another pitfall is not thinking through the literal meaning of the phrase; if you do, you will see that second to one cannot logically mean the best. Always check whether a phrase you choose truly matches the intended meaning in both literal and idiomatic senses.

Final Answer:
The correct improvement is second to none, giving: Usain Bolt is second to none as an athlete.