To understand what happens when a parameter in a procedure is declared ByVal, the user needs to have knowledge of programming concepts and specifically the concept of passing arguments to procedures.

When a parameter is declared ByVal, it means that a copy of the argument is sent to the procedure. This means that any changes made to the parameter inside the procedure will not affect the original argument in the calling code.

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

A. Only arguments of numeric data types are allowed: This option is incorrect. When a parameter is declared ByVal, it is not restricted to only numeric data types. It can be used with arguments of any data type.

B. A reference to the argument is sent to the procedure: This option is incorrect. When a parameter is declared ByVal, a reference to the argument is not sent. Instead, a copy of the argument is sent to the procedure.

C. A copy of the argument is sent to the procedure: This option is correct. When a parameter is declared ByVal, a copy of the argument is sent to the procedure. This means that any changes made to the parameter inside the procedure will not affect the original argument in the calling code.

D. Both a and b: This option is incorrect. Option a is incorrect because arguments of any data type are allowed, not just numeric data types. Option b is incorrect because a reference to the argument is not sent when the parameter is declared ByVal.

E. All of the above: This option is incorrect. Option a is incorrect, and option b is incorrect. Only option c is correct.

Therefore, the correct answer is:

The Answer is: C