She was tired after a long day at work.
- NO CHANGE (correct answer)
- after she worked a long day
- because of a long day of work
- after the long day at work
Explanation: This question tests proper prepositional phrase usage and conciseness. The original phrase 'after a long day at work' correctly uses the preposition 'after' followed by the noun phrase 'a long day at work.' This structure is clear, concise, and grammatically correct. Choice B adds unnecessary words and changes 'a long day' to 'she worked a long day,' making it wordier. Choice C uses 'because of,' which changes the meaning from temporal to causal. Choice D adds 'the' unnecessarily. The original choice provides the most direct and appropriate prepositional phrase to express the time relationship.