What property of a molecular cloud does not counteract gravitational contraction?

What property of a molecular cloud does not counteract gravitational contraction?
 
  A) thermal pressure
  B) turbulent motions
  C) magnetic fields
  D) fragmentation

Question 2

What is characteristic of a main sequence star?
 
  A) It has a mass less than the Sun's.
  B) It has rapid rotation and a strong stellar wind.
  C) Nuclear fusion in the core varies due to the amount of gravitational contraction that occurs and which heavy elements are produced.
  D) The rate of nuclear energy generated in the hydrogen to helium fusing core equals the rate radiated from the surface.
  E) All of the above are correct.

Question 3

In the halo, we do NOT find:
 
  A) tidal streams.
  B) globular clusters.
  C) small satellite galaxies.
  D) spiral arms.
  E) old white dwarfs.

Question 4

Why do researchers believe that asteroids in the asteroid belt are primal rocks that did not merge into a planet?
 
  A) The total mass of the asteroids in the asteroid belt is much smaller than that of any terrestrial planet in our solar system.
  B) The differences in chemical compositions of the asteroids are too large for them to have originated in a single body.
  C) Jupiter's gravity could have prevented these objects merging into a single body.
  D) All of the above.
  E) None of the above.

Question 5

A hydrogen atom consists of an electron and a(n):
 
  A) proton.
  B) ion.
  C) neutrino.
  D) neutron.
  E) lepton.