Which of the following SQL commands is used to retrieve data?

Answer: Option C

The SQL command used to retrieve data from a database is SELECT. Here's a brief explanation of each option:

Option A: DELETE
The DELETE command is used to remove data from a database table, not to retrieve it.

Option B: INSERT
The INSERT command is used to add new records or data into a database table, not to retrieve existing data.

Option C: SELECT
The SELECT command is specifically designed for retrieving data from one or more tables in a database. It is used to perform queries and retrieve records that match specified criteria.

Option D: JOIN
The JOIN clause is used in conjunction with the SELECT statement to combine data from multiple tables. While it is a crucial part of querying data, it is not used by itself to retrieve data; it is used to retrieve data from multiple related tables.

So, the correct SQL command to retrieve data is Option C: SELECT.