Decide whether the sentence "They were all astonished at the team's dramatic success in the competition." needs any improvement; if not, choose "No improvement".

Introduction / Context:
This sentence improvement question examines whether the given sentence is already correct and idiomatic or whether one of the suggested alternatives is better. The sentence describes a group of people reacting to their team's dramatic success in a competition. You must read it carefully and compare it with the alternatives.

Given Data / Assumptions:
Original sentence:

• They were all astonished at the team's dramatic success in the competition.

Options:

• were astonished at all
• had all astonished by
• had been all astonished on
• No improvement

We assume a normal past tense narrative about a completed event.

Concept / Approach:
The phrase were all astonished at is a standard way of expressing collective surprise about something. The preposition at is correctly used with astonished when referring to the cause of surprise. The noun phrase the team's dramatic success in the competition is also well formed. We must check if any suggested alternative improves grammar or clarity. In this case, all alternatives introduce grammatical errors, so the original is best.

Step-by-Step Solution:
Step 1: Examine the structure They were all astonished at. The verb were matches the plural subject they, and the adverb all correctly indicates that every member of the group shared the reaction. Step 2: The preposition at is correctly used to introduce the cause of astonishment: at the team's dramatic success in the competition. Step 3: Now test Option A, were astonished at all. This changes the word order to They were astonished at all, which removes the emphasis on all of them and is unidiomatic. Step 4: Test Option B, had all astonished by. They had all astonished by the team's dramatic success is grammatically wrong, because astonished would need to be a passive form (had all been astonished) and the preposition by is not the usual choice here. Step 5: Test Option C, had been all astonished on. They had been all astonished on the team's dramatic success is incorrect, because on is not the right preposition, and the word order feels awkward. Step 6: Since the original sentence is grammatically correct and idiomatic, and all alternatives introduce errors, Option D, No improvement, is the right choice.

Verification / Alternative check:
Compare with standard patterns: They were all surprised at the news or They were all shocked at his behaviour. In both examples, we use were all + adjective + at + cause. The question sentence mirrors this exact pattern: were all astonished at the team's dramatic success. Therefore, the structure is appropriate and natural.

Why Other Options Are Wrong:
Option A disturbs the natural placement of all and weakens the meaning. Option B incorrectly uses the past perfect without the necessary passive auxiliary been and uses by where at is more natural. Option C combines an unnecessarily complex tense with the wrong preposition on, making the sentence clumsy. None of these options improve clarity or correctness.

Common Pitfalls:
Students sometimes feel that exams always require a change and hesitate to choose No improvement. However, many questions are designed to test whether you recognise a sentence that is already correct. Another pitfall is getting confused by the placement of all. In English, we often say They were all astonished, which is exactly what the original sentence does correctly.

Final Answer:
The sentence is already correct, so the right choice is No improvement.