$f(x) = x – [x]$
$f(x)$ gives nothing but the fractional part of $x.$
Now, as we move up the number line between two consecutive integers say $a$ and $a+1$.
The value of $f(a)$ starts from $0$ and grows linearly till the consecutive integer and just before $x=a+1$(left neighbourhood of $a+1$) it tends to the value $1.$
Between $a$ and $a+1,$ the graph grows linearly from $0$ to $1$.
But, when at $x=a+1,$ the value comes back to $0$ and same linear graph continues between the next two consecutive integers and so on.
So, Answer C) linearly increasing function between two integers.