Input validation (D)is the most effective way to preventinjection attacks, such asSQL injection, XSS, etc. It ensures that only correctly formatted and expected inputs are processed by the application.
This is clearly identified underDomain 2.3: Application security techniques, whereinput validationis listed as aprimary defense against injection attacks.
Reference: CompTIA Security+ SY0-701 Objectives, Domain 2.3 - "Input validation: Prevents injection and malformed data attacks."