To develop an application that includes both secured and non-secured web pages, it is important to have the login page SSL (Secure Sockets Layer) enabled in order to protect sensitive user information. The SSL protocol is used to establish a secure and encrypted connection between the user's web browser and the web server.

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

A. MITM proxy can be used to change the URL to a non-secured one - This option is a possible security vulnerability. A Man-in-the-Middle (MITM) attack can be used to intercept the user's traffic and redirect them to a non-secured URL. However, enabling SSL on the login page does not directly mitigate this threat.

B. If the login page is not SSL enabled, the credentials will be transmitted in plain text to the web server and Attacker can sniff the credentials supplied by the user - This option is correct. If the login page is not SSL enabled, the credentials supplied by the user will be transmitted in plain text, which can be sniffed by attackers. This can lead to sensitive information such as usernames and passwords being compromised.

C. Firewall logs will have the credentials in plain text - This option is incorrect. Enabling SSL on the login page does not directly affect the firewall logs. Firewall logs can capture network traffic, including login credentials, regardless of whether SSL is enabled or not.

D. Proxy logs will have the credentials in plain text - This option is also correct. If SSL is not enabled on the login page, the credentials supplied by the user will be transmitted in plain text, which can be captured by proxies. This can lead to sensitive information such as usernames and passwords being compromised.

Therefore, the correct answer is:

The Answer is: B. If the login page is not SSL enabled, the credentials will be transmitted in plain text to the web server and attacker can sniff the credentials supplied by the user.