What part of a comet has only been seen by a space probe?

What part of a comet has only been seen by a space probe?
 
  A) meteoroid trail
  B) dust tail
  C) ion tail
  D) coma
  E) nucleus

Question 2

How could the distance measurements based on white dwarf supernovae be independently validated (or invalidated)?
 
  What will be an ideal response?

Question 3

One energy source for brown dwarfs is:
 
  A) hydrogen fusing to helium.
  B) helium fusing to carbon.
  C) iron core collapse.
  D) helium-3 fusing to helium-4.
  E) deuterium fusing to helium-3.

Question 4

Most stars are born in clusters containing thousands of stars.
 
  Indicate whether the statement is true or false

Question 5

How is Einstein's famous equation, E= mc2, important in understanding the Sun?
 
  A) It explains the fact that the Sun generates energy to shine by losing some 4 million tons of mass each day.
  B) It explains why the Sun's surface temperature is about 6,000C.
  C) It explains why the Sun is so massive.
  D) It explains why the Sun has a magnetic field strong enough influence the atmospheres of the planets.

Question 6

The tail of a comet always points:
 
  A) toward the Sun and disappears at perihelion.
  B) toward Earth and never varies.
  C) away from the Sun and disappears at perihelion.
  D) away from the Sun and becomes longest and brightest at perihelion.
  E) in the direction of the comet's motion.