homework5: https://ningjingsun.github.io/pui-repo/homework_5
homework6a: https://ningjingsun.github.io/pui-repo/homework_6a
homework6b: https://ningjingsun.github.io/pui-repo/homework_6b
homework7&8 https://ningjingsun.github.io/pui-repo/homework_8/overview.html