part 1.1: https://www.mediafactory.org.au/shijie-luo/2019/04/27/assignment2-part-1-1/ part 1.2: https://www.mediafactory.org.au/shijie-luo/2019/04/27/part-1-2/ part 2   : https://www.mediafactory.org.au/shijie-luo/2019/04/27/part-2/ part 3   : https://www.mediafactory.org.au/shijie-luo/2019/04/29/part-3-2/ part 4   : https://www.mediafactory.org.au/shijie-luo/2019/04/27/part-4/