Uranium,thorium,and the Radioactive Isotope of Potassium Cannot Supply the Heat

Uranium,thorium,and the radioactive isotope of potassium cannot supply the heat to melt small planetesimals,but the existence of iron and achondrite (stone) meteorites indicates that some asteroid sized bodies did melt inside.This is thought to be because short lived,intensely radioactive aluminum 26 atoms

A) were much more abundant in the solar nebula at the location where the asteroids formed.
B) were not present in the solar nebula at the location where the asteroids formed.
C) are only found in the outer layers of asteroids and not in the core.
D) are very volatile and evaporated from the asteroids before they could decay.
E) are only found on rocks that formed on the earth and in no other celestial objects.