Identify the underlined portion of the sentence that contains an error, if any, and select the most suitable replacement from the choices provided. If the original wording is grammatically sound, select 'No improvement needed'.

Without a reasons to stay in the city, the tourists departed for destinations more appealing to nature lovers.

The correct answer is Without a reason to stay in.

Step-by-step Explanation:

1. Analyze the original sentence:
The original sentence reads: "Without a reasons to stay in the city, the tourists departed for destinations more appealing to nature lovers."

2. Identify the grammatical error:
The phrase contains the indefinite article "a", which must be followed by a singular noun. However, "reasons" is a plural noun. Combining "a" with "reasons" is grammatically incorrect. It should either be "Without a reason" (singular) or "Without reasons" (plural).

3. Evaluate the options:
- Without a reason to stay in: Correctly uses the singular noun "reason" with the singular article "a", preserving the appropriate preposition "in" for "the city".
- With a reasons to stay in: Incorrect because it still uses "a" with the plural noun "reasons" and changes the meaning with "With".
- Without a reasons to stay by: Incorrect because it retains the grammatical error "a reasons" and uses an inappropriate preposition "by".
- Without a reasons to stay on: Incorrect because it retains the grammatical error "a reasons" and uses an inappropriate preposition "on".
- No improvement needed: Incorrect because the original phrase contains an error.

4. Conclusion:
Replacing the underlined portion with "Without a reason to stay in" yields a grammatically sound sentence: "Without a reason to stay in the city, the tourists departed for destinations more appealing to nature lovers."