As a star forms, the photosphere first appears:
A) when the planetary nebula is expelled.
B) when the protostar forms.
C) when contraction slows down.
D) when nuclear fires ignite.
E) when the star reaches the main sequence.
Question 2
The particles which enter into chemical reactions are the atom's:
A) protons.
B) neutrons.
C) positrons.
D) electrons.
E) mesons.
