B is true. Which makes sense; for a function to "increase", each successive value has to be greater than the last.

The interval part of the question is only there to force you to order the way you choose the numbers. x1<x2 means "The first x value has to be less than the second", and x1>x2 means "The first choice has to be greater than the second".

So if x-values increase across a domain, and the range increases in response, previous x-values have to be lesser (x1<x2) and the function has to return a first value (fx1) less than (<) the second (fx2).