The correct answer is **but** (Option 4). **Comprehensive Derivation:** The correct answer is "but" Explanation & Key Takeaways: • In the above question, we have to fill in the most appropriate conjunction. • Option 4) is correct because the conjunction "but" is the most appropriate choice in this sentence as it is used to show contrast or to express a change of direction. The first part of the sentence states that the speaker has been waiting for a long time, and the second part of the sentence states that the speaker's friend has not turned up, indicating a contrast between the two actions. • Option 1) "and" is incorrect because it does not express contrast or a change of direction, instead it indicates that the two actions are happening at the same time. • Option 2) "though" is incorrect because it indicates that the two actions are happening simultaneously, but there is no evidence to suggest that both actions are happening at the same time. • Option 3) "moreover" is incorrect because it is used to indicate a further point or Related Concepts: , but there is no Related Concepts: being provided in this sentence. • Thus, as per the above explanation the correct answer is Option 4. Correct answer: I have been waiting here for a long time, but my friend has not turned up. **Option Elimination:** • **Option 1 (and)**: Incorrect distractor. • **Option 2 (though)**: Incorrect distractor. • **Option 3 (moreover)**: Incorrect distractor. • **Option 4 (but)**: Correct Answer; accurate according to canonical reference. **Exam Trap:** Be careful of misleading distractors and subtle terminology differences. Verify core properties before selecting your answer. **Memory Booster:** Core mnemonic rule: but corresponds to Option (4).