Which command is used to display all the existing tables in a database?

Answer: Option A

This question is about finding all the tables in a database. Databases are like giant filing cabinets for information, and tables are like folders inside those cabinets.
We need a command that tells MySQL to open the cabinet and show us all the folders.
Let's look at the options:
Option A: SHOW TABLES - This is the correct command. It tells MySQL to list all the tables in the current database.
Option B: SHOW TABLE - This is incorrect. It's missing the "S" at the end.
Option C: SHOW - This is incorrect. It's too general and doesn't specify what we want to show.
Option D: None of the mentioned - This is incorrect because we found the right command in Option A.
So the answer is Option A: SHOW TABLES.