根据下面各题括号里汉语的提示和句子的意思,写出恰当形式的英语单词，每空格只写一个单词。( 共5小题;每小题1分,满分5分)
Look at the sign, “No        !”(游泳)
One of my       (脚) is becoming bad.
Can I ask a       (帮助)？
      (十二月) is the twelfth month in a year.
Which book is      ( 便宜), this one or that one?