In LSM trees, what is 'Space Amplification'?

1. A The ratio of total system RAM to persistent disk storage, which determines the maximum size of the buffer pool for active indexing operations.
2. B The physical expansion of the primary data files that occurs when multiple non-clustered indexes are added to a single table for performance.
3. C The growth rate of the database's internal transaction and debug logs during periods of exceptionally high write-concurrency and throughput.
4. D The ratio of physical disk space used versus the actual live data size, caused by old record versions persisting until background compaction runs.