Which pgvector operator matches an HNSW index built with vector_cosine_ops?

1. A <->
2. ✓ B <=> (correct answer)
3. C <#>
4. D @>

Shortcut: The index operator class must match the query operator. vector_cosine_ops serves <=> (cosine distance); vector_l2_ops serves <->; vector_ip_ops serves <#>. A mismatch causes a sequential scan.