In this English sentence improvement question, choose the best option to replace the word in brackets in the sentence "He is an atheist (yet) he goes to church every Sunday", or select "No improvement" if the sentence is already correct.

Introduction / Context:
Sentence improvement questions test a learner ability to select conjunctions and connectors that correctly show the relation between two ideas. The given sentence is He is an atheist yet he goes to church every Sunday. The contrast here is important, because an atheist is a person who does not believe in the existence of God, while going to church regularly is normally associated with religious belief. The question asks whether the bracketed word yet needs improvement, or whether it is already the correct choice in this context.

Given Data / Assumptions:
- The sentence under examination is: He is an atheist yet he goes to church every Sunday. - The bracketed word yet may be replaced by another connector. - The options available are because, and, however, and no improvement. - The aim is to preserve the contrasting relationship between the two clauses.

Concept / Approach:
Connectors in English signal different logical relations. Because introduces reason or cause. And usually joins similar or related ideas without contrast. However is a sentence level connector that usually comes at the beginning of a new sentence or after a semicolon. Yet is a coordinating conjunction that introduces a surprising contrast, similar to but. Since the sentence intends to show that his regular church visits are surprising given that he is an atheist, a contrastive connector is required. We must choose the option that most naturally and correctly expresses this contrast in one sentence.

Step-by-Step Solution:
Step 1: Check the meaning of the first clause: He is an atheist. This indicates lack of belief in God. Step 2: Check the second clause: he goes to church every Sunday. This suggests regular religious attendance. Step 3: Decide that the intended relationship between the clauses is one of contrast or unexpected combination, not simple cause or addition. Step 4: Evaluate because. This would suggest that he goes to church every Sunday as a result of being an atheist, which does not make logical sense. Step 5: Evaluate and. This would simply add information without highlighting the surprising contrast. Step 6: Evaluate however. This word is contrastive but functions better at the start of a new sentence, for example, He is an atheist. However, he goes to church every Sunday. Step 7: Recognise that yet is already a correct coordinating conjunction for contrast inside a single sentence, similar to but.

Verification / Alternative check:
We can try rewriting the sentence with similar meaning: He is an atheist but he goes to church every Sunday. This proves that a coordinating conjunction of contrast is needed. Since yet functions almost like but in such contexts, He is an atheist yet he goes to church every Sunday is natural and grammatically correct. If we insert however without adjusting punctuation, as in He is an atheist however he goes to church every Sunday, the sentence sounds awkward and less standard. Therefore the best answer is that no improvement is required.

Why Other Options Are Wrong:
Option A, because, would wrongly suggest that his atheism is the reason why he goes to church, which distorts the meaning. Option B, and, fails to show any contrast, and the sentence would lose its sense of surprise. Option C, however, is mainly used as a conjunctive adverb at the start of a second sentence or after a semicolon, so it does not fit smoothly in the given structure without punctuation changes.

Common Pitfalls:
Students often rush to replace the given connector just because a more formal sounding word like however appears in the options. Another common mistake is to ignore punctuation and the difference between coordinating conjunctions such as but and yet, and conjunctive adverbs such as however and therefore. For sentence improvement questions, it is essential to imagine how native speakers usually form such sentences in real communication. In this case, the original wording is already natural and correct, so the safest and most accurate choice is to leave it unchanged.

Final Answer:
The correct answer is no improvement.