To solve this question, the user needs to have knowledge of error handling in SQL.

Now, let's go through each option and explain why it is right or wrong:

A. RAISE_ERROR: This option is not a valid procedure to create a custom error message in SQL. RAISE_ERROR is not a standard Oracle SQL function.

B. SQLERRM: This option is not a procedure to create a custom error message, but it is a function that returns the error message associated with the most recently raised error exception. It is not used to raise custom exceptions.

C. RAISE_APPLICATION_ERROR: This option is correct. RAISE_APPLICATION_ERROR is a procedure used to create a customized error message in Oracle SQL. It allows an application to raise an error with a user-defined error message and error number.

D. RAISE_SERVER_ERROR: This option is not a valid procedure to create a custom error message in SQL. RAISE_SERVER_ERROR is not a standard Oracle SQL function.

Therefore, the correct answer is: C. RAISE_APPLICATION_ERROR