Modify the Chinese words about 1~9, ten, hundred, thousand.
[Modify exercise]
modify the content of place_value_concept.html
[Modify exercise]
limit the input to only 1 number.
[Modify exercise]
Fix bug.
[Modify exercise]
modify <br>--><br />
[modify exercise]
modify the case8 in place_value_concept.html
[modify exercise]
change the input type statement.
Merge branch 'place_value_concept'