1. Some products, such as GPS, iPhone 7, etc., are currently out of stock in Bestbuy. Some customers want to be notified if these products become available again. Please create a sequence diagram and a class diagram for the analysis and design.

3. Imagine that you will develop a web system for a rural area, which only has very slow Internet connection. As downloading images is pretty time consuming, you want to make a place holder for the image when initializing a web page. We want to show the text portion as soon as possible. The real images are displayed after the text portion has been downloaded. This strategy is good because users have something to see when they try to open a web page. Otherwise, they will lose patience if they have to wait for a long time to see the web page. Please use the class diagram to make the design.