What sets the association between one or more MyISAM tables and the named key cache?

This question asks about how you tell MySQL which key cache to use for a MyISAM table. Key caches are used to store information about your tables' indexes, speeding up data access.

Let's break down the options:
Option A: BEGIN
This is used to start a transaction in MySQL, not for setting key caches.
Option B: CACHE INDEX
This is the correct answer! The CACHE INDEX command is used to explicitly set the key cache for a MyISAM table.
Option C: ALTER DATABASE
This is used to modify the structure of a database itself, not individual table settings like key caches.
Option D: ALTER EVENT
This is used to modify scheduled events within MySQL, unrelated to key caches.

In summary, the correct answer is Option B: CACHE INDEX.