You work as an Enterprise Application Developer for ABC Inc.

You work as an Enterprise Application Developer for ABC Inc. The company uses Visual Studio 2008 as its application development platform. You create a web application using .NET Framework 3.5. You have created a form named Form1. You have added Textbox controls for taking Name, Address, and Phone Number of user as input in Form1. You want to ensure that a user enters a value in the Name field. Which of the following validation server controls will you use to accomplish the task?