One Way to Probe the Rate of Nuclear Reactions in the Center

One way to probe the rate of nuclear reactions in the center of the Sun is by studying ______ produced because _____________.

A) positrons; they annihilate into gamma rays of very specific energies
B) neutrinos; they pass out of the Sun without undergoing a random walk
C) heavy hydrogen; it has different spectral lines than normal hydrogen
D) wave motions; they can be measured at the Sun's surface