Whether the Universe is open, closed or flat depends, on the ___________ of the Universe.

Whether the Universe is open, closed or flat depends, on the ___________ of the Universe.
 
  a. luminosity
  b. density
  c. temperature
  d. radius
  e. rotation rate

Question 2

Why can't lower-main-sequence stars become giant stars?
 
  What will be an ideal response?

Question 3

Seeds around which galaxies, clusters and walls grew may have been ___________ before inflation and recombination.
 
  a. caused by hot dark matter
  b. caused by baryons
  c. the result of the separation of the electromagnetic and weak forces
  d. the result of freezing water molecules shortly after the Universe became transparent to photons
  e. caused by initially tiny quantum mechanical fluctuations in space-time