While all the options can help reduce the risk of data leakage, providing education and guidelines to employees on the use of social networking sites would be the most effective. This is because it directly addresses the issue at hand - the use of social networking sites for business purposes1. Education and guidelines can help employees understand the risks associated withsocial media use and teach them how to safely and responsibly use these platforms for business purposes1. This includes understanding privacy settings, recognizing phishing attempts, and knowing what information should not be shared on these platforms1.
References:
10 Social Media Guidelines for Employees in 2023 - Hootsuite

Comprehensive and Detailed In-Depth Explanation:A Web Application Firewall (WAF) (A) is the best control to mitigate SQL injection attacks because it can detect and block malicious SQL queries before they reach the application. WAFs analyze incoming requests, filter SQL injection attempts, and provide an additional layer of security for web applications.
Other options:
* SQL server hardening (B) improves security but does not specifically address SQL injection.
* Patch management (C) is necessary but does not provide immediate protection against new SQL injection attacks.
* Physical controls (D) are unrelated to application-layer threats like SQL injection.
Reference: ISACA CISA Review Manual, Information Security