Question

what should a scientist do i there are two or three different explanations for what happened in an experiment?

Answer 1

refine the parameters tested to rule out some of the possibilities

Answer 2

The other thing to do is to set up some control experiments to rule out other possibilities: in other words set something up that is identical except for one thing so that you know what caused the difference. If the problem was that an enzyme -catalysed reaction was faster at a higher temperature with more enzyme then an identical experiment at the same temperature would show whether the amount of enzyme was important.