下面是关于函数f（x）=|x﹣{x}|的四个命题：①函数y=f（x）的定义域是R，值域是 $0,\frac{1}{2}$ ；②函数y=f（x）的图象关于直线 $x=\frac{k}{2}\left(k\in Z\right)$ 对称；③函数y=f（x）是周期函数，最小正周期是1；其中正确的命题序号是____．

   On the evening of October 7, Li Feng was watching TV while his mother was ____ b      cooking supper in the kitchen. ____ S       the telephone rang. Li Feng ____ q     picked it up to____ a        the call. It was from a good friend of his____ m     . She wanted to say “Happy Birthday” to his mother. "Today is Mother's birthday, but I have already____       f_____all about it. Mother gives me a lot of____ l      and care while I didn't care for her____ e    . From now on, I must always____ r     this, ____ s     my love to her and care for her enough,” Li Feng thought to himself, feeling a little ashamed(惭愧的).