Which PostgreSQL extension enables vector similarity search for AI embedding storage and retrieval?

1. A pg_trgm
2. B pgcrypto
3. ✓ C pgvector (correct answer)
4. D PostGIS

Shortcut: pgvector adds a vector data type and index types (IVFFlat, HNSW) to PostgreSQL, enabling efficient approximate nearest neighbour search over high-dimensional embeddings.