Hmm, maybe it's a trick question, but logically, how does zero change with time? If your function is zero at all t, then I would assume yes, the answer is zero.
If this is for a lower level calc class, that is probably the answer. If it's higher level, then I am most likely wrong. :)
If dt is a number, then 0/dt= 0. If dt is a differentianl, then 0/dt is simply meaningless. I wonder if you haven't got a fraction in which the numerator has a limit of 0? If the denominator is going to "dt", a differential, then, essentially, you have a "0/0" situation in which the limit depends on exactly how that limit is taken.
Please tell us what the problem was from which you got "0/dt".