What Is the Solution to the Solar Neutrino Problem

What is the solution to the solar neutrino problem?

A) Not all fusion reactions create neutrinos.
B) The Sun is generating energy other than by nuclear fusion.
C) We did not know how to detect neutrinos.
D) The electron neutrinos created in the Sun's core change into another type of neutrino that we did not detect.
E) The Sun is generating much less energy than we think it is.