The MySQL server used in its client/server architecture is . . . . . . . .

This question asks about the server component used in the MySQL client/server architecture. MySQL uses a client/server model which means there are separate programs for the server and client.

The server is responsible for managing the database, processing queries, and providing data to clients.

Out of the given options, mysqld is the correct answer. mysqld is the MySQL server daemon, which is responsible for running the MySQL server and providing database services.

The other options (mysqla, mysqlb, mysqlc) are not valid server components in MySQL.

So the final answer is Option D: mysqld.