The Terrestrial Planets Are Made Almost Entirely of Elements Heavier

Multiple Choice

The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did these elements come from?

A) They were produced by stars that lived and died before our solar system was born.
B) They have been present in the universe since its birth.
C) They were made by chemical reactions in interstellar gas.
D) They were produced by gravity in the solar nebula as it collapsed.