We have to describe with one word the behaviour of the function in the interval [2,6].
We can see that, for increasing values of x, the values of the function y=f(x) also increase without exception, so we can describe its value as increasing in this interval.
For any value xa>xb in the interval, we have f(xa) > f(xb), which is the formal demonstration that the function is always increasing in this interval.
Answer: C. increasing.
