John Was Watching the Night Sky on a Clear Evening

John was watching the night sky on a clear evening in November.He noticed that sometimes when he looked directly overhead he could detect a very faint star.A few minutes later it seemed that the star had disappeared, and then it "appeared" again.In this case, it is very likely that the light from the star was

A) just below John's level for perceptual invariance.
B) producing action potentials that were too weak to reach the terminal buttons.
C) just at John's absolute threshold for light.
D) producing inhibitory synapses rather than excitatory synapses.