Henrietta Leavitt discovered the period-luminosity relationship for ____________________. (Fill in the blank)

Henrietta Leavitt discovered the period-luminosity relationship for ____________________.
 
  Fill in the blank(s) with correct word

Question 2

That Earth ____ , evidence that Earth differentiated.
 
  a. rotates slowly
  b. has an average density that is higher than the density of the crust
  c. has a no magnetic field
  d. has a surface that is 75 water
  e. all of these

Question 3

The rotation curve of the galaxy provides evidence for the existence of the ____________________ which extends beyond the halo of the galaxy.
 
  Fill in the blank(s) with correct word