Initially, Fewer Neutrinos Were Detected Than Predicted by Theoretical Models

Initially, fewer neutrinos were detected than predicted by theoretical models because

A) neutrinos changed form to undetected types of neutrinos.
B) the wrong liquid was being used in neutrino detectors.
C) particle physicists did not understand the proton-proton chain.
D) the proton-proton chain does not actually produce neutrinos.
E) neutrinos take many years to pass out of the sun from its core.