What characteristic of a telescope controls the amount of light captured by the telescope?

What characteristic of a telescope controls the amount of light captured by the telescope?
 
  a. resolving power
 b. magnifying power
  c. size of eyepiece
 d. number of mirrors
  e. diameter of tube

Question 2

Which types of galaxies lack an ordered structure of stellar orbits?
 
  a. elliptical galaxies only
 b. spiral galaxies only
 c. irregular galaxies only
 d. elliptical and irregular galaxies
  e. spiral and irregular galaxies

Question 3

Which telescope is the largest refracting telescope in the world?
 
  a. Large Binocular Telescope
 b. Gemini-North optical telescope
 c. Very Large Array
 d. Keck telescope
 e. Yerkes Observatory refractor telescope

Question 4

In which of the following types of galaxies would you expect to find active star formation?
 
  a. elliptical galaxies only
 b. elliptical and spiral galaxies
 c. spiral galaxies only
 d. elliptical and irregular galaxies
  e. spiral and irregular galaxies