Which Redis data structure is optimal for implementing a leaderboard sorted by score?

1. A String
2. B Hash
3. C List
4. ✓ D Sorted Set (ZSET) (correct answer)

Shortcut: Sorted Sets store members with a floating-point score, sorted by score automatically. ZADD, ZRANK, ZRANGE enable efficient leaderboard operations (add score, get rank, list top N).