From an application security perspective, CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is commonly used for preventing scripted attacks. These attacks involve automated bots or scripts that try to exploit vulnerabilities in web applications. By using CAPTCHA, it becomes harder for automated bots to bypass security measures and perform malicious activities like spamming, credential stuffing, or brute-forcing.

So, the correct answer is A. To prevent scripted attacks.

Option B, "to provide biometric authentication," is not the primary purpose of CAPTCHA. Biometric authentication typically involves using unique physical or behavioral characteristics of an individual, such as fingerprints or facial recognition, to verify their identity.

Option C, "to check the color blindness of the user," is not the primary purpose of CAPTCHA either. CAPTCHA primarily focuses on distinguishing between humans and bots, and while it may include visual challenges, it is not specifically designed to check for color blindness.

Option D, "more security," is a vague statement and doesn't provide a specific reason for using CAPTCHA. While CAPTCHA does enhance security by preventing automated attacks, it is more accurate to say that it specifically targets preventing scripted attacks.

Therefore, the correct answer is A. To prevent scripted attacks.