Final answer:
When logging into the vSphere Client, the required information at the login screen is the Username and Password. This allows the user to authenticate and manage resources within the vSphere environment.
Step-by-step explanation:
When using the vSphere Client, you need to enter the following information at the login screen: Username and Password. The vSphere Client is a part of VMware's virtualization products, and it is used for managing virtual machines and other components of vSphere environments. To gain access to manage these resources, the client requires authentication credentials. Therefore, the correct answer to the question is A) Username, Password.