What was the key physical property in determining the two categories of planets during solar system ...

What was the key physical property in determining the two categories of planets during solar system formation?
 
  a. pressure
 b. gravity
 c. density
 d. momentum
  e. temperature

Question 2

The horizontal axis (X-axis) of the Hertzsprung-Russell diagram is labeled with _______________.
 
  Fill in the blank(s) with correct word

Question 3

According to solar nebula theory, what is the first step in planetesimal formation?
 
  a. heating
 b. flattening
 c. accretion
 d. condensation
 e. gravitational collapse

Question 4

The least common type of star is a(n) ____.
 
  a. white dwarf
 b. lower main sequence
  c. upper main sequence
  d. giant
 e. supergiant