Improve the following sentence, if necessary, by choosing the most appropriate option: "I regret for using objectionable words against a man so mighty."

Introduction / Context:
This question checks your understanding of correct verb patterns with "regret" and common collocations in formal English. The original sentence contains an extra preposition that makes it grammatically awkward. You need to select the option that expresses the idea of feeling sorry for past language, while maintaining correct structure and tone.

Given Data / Assumptions:
- Original sentence: "I regret for using objectionable words against a man so mighty."
- The speaker wishes to express deep regret for having used inappropriate or rude words.
- The options provide different verbs and preposition combinations, and a "No improvement" choice.
- We must choose the most natural and grammatically accurate version.

Concept / Approach:
In standard English, "regret" can be followed directly by a gerund without any preposition: "regret doing something". The structure "regret for doing" is not idiomatic when the gerund follows immediately. Preposition "for" is used with "sorry" as in "sorry for doing something". Therefore, the best correction is to remove the unnecessary "for" while keeping "regret" and the gerund phrase "using objectionable words".

Step-by-Step Solution:
Step 1: Focus on the phrase "regret for using". Step 2: Recall correct patterns: "regret doing", "regret having done", or "sorry for doing". Step 3: Notice that "regret for using" is not a standard combination. Step 4: Remove the extra preposition and say "I regret using objectionable words against a man so mighty." Step 5: Compare with options. Option C matches this corrected sentence exactly.

Verification / Alternative check:
Consider option B: "I am sorry for using objectionable words against a man so mighty." This is also grammatically correct and natural. However, the test is about improving the given sentence by adjusting as little as necessary, and the verb "regret" in the stem can be kept with correct structure. Option C does exactly that. Option A "repent for" is grammatically odd in this construction, and "No improvement" is invalid because the original pattern "regret for using" is non standard.

Why Other Options Are Wrong:
- "repent for using": sounds unnatural; "repent of" is more traditional, and "repent" is often used in religious contexts rather than everyday regret for speech.
- "am sorry for using": grammatically correct but changes the main verb without need; still less faithful to the original wording than option C.
- "No improvement": wrong because the combination "regret for using" is incorrect in standard English.

Common Pitfalls:
A frequent mistake is to insert "for" automatically after verbs related to emotion. Learners often say "regret for doing", "apologise for", "sorry for", and confuse which verbs do and do not take "for". Always remember that "regret" is directly followed by a gerund, for example "regret saying that", while "sorry" normally needs "for", as in "sorry for saying that".

Final Answer:
The best improved sentence is I regret using objectionable words against a man so mighty.