Answer:
observable
Step-by-step explanation:
In order for an experiment to succesfully take place, the experiment must be controlated, observable, and repeatable, this means that under certain circumstances that you are able to control, you can observe an event and investigate it. It has to be observable in order to gain and gather information about the event and with this be able to come up with a conclusion of factor that make it possible and the consequences that the given event has.