Which search mode uses natural language search as a subroutine?

Answer: Option C

This question is about how MySQL searches for information. Think of it like searching for a book in a library.

Natural language mode lets you search using words like you would in a normal sentence. It's like asking a librarian, "Can you find me a book about cats?".

Boolean mode uses special words like "AND", "OR", and "NOT" to refine your search. It's like giving the librarian a list of specific keywords to use.

Query expansion is a technique that tries to find related words and phrases to help you get more results. Imagine the librarian suggesting other books on related topics.

Cross mode isn't a standard search mode in MySQL.

So, the answer is Option A: Natural Language. Natural language mode is designed to understand your search terms like you would speak them.