Sagittarius A has a mass of _____.

Sagittarius A has a mass of _____.
 
  A) 3 million Earth masses
  B) 4 million solar masses
  C) 5 million Earth masses
  D) 6 million solar masses

Question 2

Which of the following is true of atoms in the Universe?
 
  A) Most of the iron in your body was produced by nuclear fission reactions.
  B) Most of the calcium atoms in your bones were not assembled inside stars.
  C) The iodine atoms were not formed during the violent deaths of rare massive stars.
  D) The gold and silver atoms were created in a few moments during supernova explosions.

Question 3

Astronomers try to reconstruct our Galaxy's past from _____.
 
  A) its spherical component
  B) its disk component
  C) its spiral arms
  D) the stars of neighboring galaxies

Question 4

One of the reasons that gold is a rare element is that:
 
  A) it has a very low atomic mass.
  B) it has a very low atomic number.
  C) gold atoms were absorbed during supernova explosions.
  D) gold atoms are made only by short-lived nuclear reactions.