The Vau U PROBLEM 3 (2*10 points) (I) What is CSS and explain why people use CSS. (2) Write out the recommended minimal structure of an HTML5 document, PROBLEM 4 ( 3*10 points) (1) What is the DOM? How is it useful? (2) For many HTTP requests, GET and POST both work well. Describe two circumstances in which POST would be preferred over GET without taking speed or efficiency into account. (3) In your opinion, which programming language is better, PHP or Javascript? List 2 specific reasons to justify your choice