Fix the folder problems.
The second week homework final version. not difficult but
interesting.By the way, the home page is a little ugly…
Merge branch 'ex2'
Revert "Merge branch 'ex2'"

This reverts commit db292319685928347e54b44667438c3bde7b13e0, reversing
changes made to dab838d33555fc59668b6b57ed3724b03d85945b.
Having something wrong with my previous branch Ex2…I guess I did a
wrong operation. So I upload again…