In the context of spectral classes, which of the following statements is true of T dwarfs?

In the context of spectral classes, which of the following statements is true of T dwarfs?
 
  A) They are a spectral class of red giant stars.
  B) They are hotter than L dwarfs.
  C) They are a spectral class of white giant stars.
  D) They are fainter than L dwarfs.

Question 2

In the context of the Hertzsprung-Russell (H-R) diagram, which of the following statements is true of the most massive main-sequence stars?
 
  A) They are the reddest stars.
  B) They are the coolest stars.
  C) They are the hottest stars.
  D) They are the faintest stars.

Question 3

In the context of the triangulation method, to find the distance to a star, astronomers use a very long baseline, which is _____.
 
  A) the size of Earth's orbit
  B) the diameter of Earth's orbit
  C) three times the radius of Earth's orbit
  D) double the size of Earth's orbit