Upper-main-sequence stars, more massive than the Sun, fuse hydrogen by a process called the _____. ...

Upper-main-sequence stars, more massive than the Sun, fuse hydrogen by a process called the _____.
 
  A) proton-proton chain
  B) carbon-nitrogen-oxygen cycle
  C) zero-age main sequence
  D) proton-neutron chain

Question 2

Which of the following statements is true regarding the stars in a stellar association?
 
  A) They orbit a common center of mass.
  B) They were not formed together.
  C) They are gravitationally bound to one another.
  D) They drift away from each other in a few million years.

Question 3

_____ is the process in which dust scatters blue light out of starlight and makes the stars look redder.
 
  A) Interstellar reddening
  B) A blueshift
  C) A redshift
  D) Cosmic reddening