Final answer:
The most valid prediction is that the policeman will detect any unusual activities due to the quiet and emptiness of the streets combined with his watchfulness.
Step-by-step explanation:
Based on the descriptive excerpts provided about the policeman on his beat, the most valid prediction for what will happen in this story is that the policeman will be aware of anything unusual, as hinted at by the quiet, empty streets. The text emphasizes the officer's impressiveness, watchfulness, and the well-nigh deserted avenue, suggesting his readiness to detect any disturbance. Furthermore, the setting described indicates that the area is not bustling with activity, which allows the officer to focus more intently on any potential anomalies.