A security engineer is assisting a developer with input validation, and they are studying the following code block: 

The security engineer wants to ensure strong input validation is in place for customer-provided account identifiers. These identifiers are ten-digit numbers. The developer wants to ensure input validation is fast because a large number of people use the system. Which of the following would be the BEST advice for the security engineer to give to the developer? 

Answer options:

A. Replace code with Java-based type checks
B. Parse input into an array
C. Use regular expressions
D. Canonicalize input into string objects before validation

C