If an event $E$ has only one sample point of a sample space, it is called a ______:

1. Simple (or Elementary) Event: An event consisting of only one outcome of the experiment.2. Compound Event: An event consisting of more than one sample point.3. Sure Event: An event that contains all sample points (probability is 1).4. Impossible Event: An event with no sample points (probability is 0).Since the question specifies "only one sample point", it is a Simple event.