A part of the sentence is underlined. Choose the alternative that best improves the underlined part, or select "No improvement" if the sentence is already correct: "I was impressed of it."

Introduction / Context:
This sentence improvement question focuses on correct prepositional usage after certain adjectives, in this case the adjective "impressed". The sentence "I was impressed of it" contains a preposition that does not collocate properly with "impressed". You must choose the preposition that is normally used in standard English or decide that no change is needed.

Given Data / Assumptions:

- Original sentence: "I was impressed of it." - Underlined preposition: "of". - Options: "by", "on", "for", "No improvement". - The intended meaning is that something made a strong positive impact on the speaker.

Concept / Approach:
In standard English, the usual pattern is "impressed by" someone or something, or "impressed with" someone or something. The preposition "of" is not used after "impressed" in this sense. Therefore, "I was impressed by it" is the correct and idiomatic way to express that "it" created a good impression on the speaker. The other prepositions do not match the typical collocation.

Step-by-Step Solution:
Step 1: Recall examples of correct usage: "I was impressed by her performance" or "We were impressed by the speech". Step 2: Apply this pattern to the given sentence: "I was impressed by it." This is grammatically correct and natural. Step 3: Test "on": "I was impressed on it" does not form a recognised collocation and sounds incorrect. Step 4: Test "for": "I was impressed for it" also sounds unnatural and does not carry the intended meaning. Step 5: Consider "No improvement". Keeping "of" would leave the sentence in a nonstandard form, which is not acceptable for exam level English. Step 6: Therefore, the best improvement is to replace "of" with "by" to obtain "I was impressed by it".

Verification / Alternative check:
Think of similar sentences: "The judges were impressed by the dancers" or "Everyone was impressed by the new technology". In all these examples, "by" introduces the cause of the impression. Using "of" would be wrong: "impressed of the dancers" is never used in standard English. A quick search in good quality reading material will confirm that "impressed by" and "impressed with" are the correct patterns.

Why Other Options Are Wrong:
"On" is used with verbs like "depend on" or "insist on", but not with "impressed". "For" is used in patterns like "famous for", "known for", "responsible for", but not with "impressed" in this sense. "No improvement" would incorrectly accept "impressed of", which is nonstandard. Therefore, these three options do not provide the necessary correction.

Common Pitfalls:
Many learners choose prepositions based on their first language, leading to mistakes like "impressed of" or "impressed on". A good strategy is to memorise common adjective plus preposition pairs, such as "afraid of", "good at", "interested in", and "impressed by". Regular exposure to native level writing and listening will reinforce these patterns and reduce confusion during exams.

Final Answer:
by is the correct improvement, giving the sentence "I was impressed by it."