In a composite index `(A, B)`, if specific rows have `NULL` for column B, are they included in the index?

1. A No, standard B-Tree indexes strictly exclude all rows containing a NULL value to minimize the overall physical footprint of the index file.
2. B Yes, modern B-Tree indexes typically include NULL as a sortable value, allowing the database to efficiently satisfy `IS NULL` query predicates.
3. C Only in specialized NoSQL databases, as relational systems require all indexed columns to possess a concrete, non-null value for hash-consistency.
4. D Yes, but only if the database is configured to automatically convert all incoming NULL values into empty strings or zero-value numeric equivalents.