Read the following sentence and identify the part that contains an error in standard English usage: "When I finished writing the letter, I could not help admiring myself to have achieved the impossible."

Introduction / Context:
This error spotting question tests idiomatic usage with the expression "could not help" and the correct construction to describe feeling pleased about an achievement. The sentence conveys self satisfaction after completing a difficult task, but uses an unnatural combination "admiring myself to have achieved". Examinations often check whether you can recognise such subtle idiomatic errors.

Given Data / Assumptions:
The sentence is broken into parts:
- Part (a): "When I finished writing the letter,"
- Part (b): "I could not help admiring myself to have"
- Part (c): "achieved the impossible."
- Part (d): "No error"
We need to identify which part contains the incorrect phrase or structure.

Concept / Approach:
The phrase "could not help" is typically followed by a gerund: "could not help laughing", "could not help admiring". That part is fine. The problem is the construction "admiring myself to have achieved". To express the reason for the admiration, English normally uses a preposition plus gerund pattern, such as "for having achieved the impossible". Thus the natural sentence would be "I could not help admiring myself for having achieved the impossible" or "I could not help admiring myself for achieving the impossible". The use of "to have achieved" here is non idiomatic.

Step-by-Step Solution:
Step 1: Check the time clause "When I finished writing the letter," in part (a). It is grammatically correct. Step 2: Examine part (b) "I could not help admiring myself to have". The phrase "to have" looks suspicious in this position. Step 3: Recall that we usually say "admiring myself for having achieved" rather than "admiring myself to have achieved". Step 4: Note that part (c) "achieved the impossible." is a correct phrase completing the idea of achievement. Step 5: Conclude that the error lies in part (b), specifically in the combination "admiring myself to have".

Verification / Alternative check:
Construct a corrected version of the sentence: "When I finished writing the letter, I could not help admiring myself for having achieved the impossible." Now each segment flows properly. The preposition "for" introduces the reason, and "having achieved" correctly refers to a completed action that has just occurred. This confirms that the problematic zone is in part (b) and that the intended grammar requires a preposition and a gerund, not the bare infinitive "to have".

Why Other Options Are Wrong:
- Part (a): "When I finished writing the letter," is a standard time clause and is error free.
- Part (c): "achieved the impossible." correctly completes the thought and does not contain any grammatical mistake.
- "No error": is incorrect because we have identified a clear idiomatic error in part (b).

Common Pitfalls:
Students sometimes overuse the structure "to have plus past participle" in formal contexts, assuming it always sounds advanced or correct. In reality, English has many fixed collocations where certain prepositions and verb forms are preferred. With verbs such as "admire", "criticise", "praise", and emotional reactions, it is common to use "for doing" or "for having done" rather than "to have done". Paying attention to patterns you see in well edited texts can help you avoid these subtle mistakes.

Final Answer:
The incorrect portion is I could not help admiring myself to have, that is, part (b). A correct version would be "I could not help admiring myself for having achieved the impossible."