单项选择题 You are developing a page named Products.aspx in a Web application that contains three DropDownList controls that are dynamically loaded from a SQL Server 2005 database file. The DropDownList controls represent a vendor list, a certification list, and an exam list. Certkiller .com customers use the Products.aspx page to select exams related to particular certifications on offer from a particular vendor. A Go button initiates the selection. Each DropDownList control has an associated RequiredFieldValidator control.Whenever the customer selects a vendor, and the vendor offers certifications, then the customer must also select a certification if the. If the vendor only offers exams and not certifications, the certification list should remain hidden. Whenever the customer selects a certification, the customer must also select an exam. Validation error messages should only be displayed when the Go button is clicked. You need to set properties on the vendor DropDownList control. What should you do?（）

单项选择题 You are developing a product search page named Search.aspx for Web application that will be integrated into Certkiller .coms existing e-Commerce Web site. The Search.aspx page allows customers search for products that match specific criteria. Once a product is located, you want an image of the product to be displayed. You want to use an Image control to display the image. You want to configure the Image control to display a description of the image if the image cannot be displayed in the customers Web browser. What should you do?（）

多项选择题 You create a mobile Web application. You need to use a Command control to post user input from the UI elements back to the server. What are two possible ways to achieve this goal?（）