Who invented the galaxy classes, and what three major groups did ...

[jman1234]

Who invented the galaxy classes, and what three major groups did he invent?
 
  What will be an ideal response?

Question 2

On average, how often do impacts large enough to produce mass extinction on the Earth occur?
 
  A) once every century
  B) once every million years
  C) once in Earth's history
  D) once every thousand years
  E) once every hundred million years

[randomguy133]

Answer to Question 1

Edwin Hubble divided the galaxies into S (spirals), E (ellipticals) and Irr (irregulars).

Answer to Question 2

E

[jman1234]

Excellent

[mochi09]

Wow, this really help