The large gaps in the asteroid belt (often called Kirkwood gaps) ...

[student77]

The large gaps in the asteroid belt (often called Kirkwood gaps) are caused by
 
  A) large asteroids that clear certain regions of the asteroid belt.
  B) tidal forces from Jupiter.
  C) tidal forces from the Sun.
  D) orbital resonances with Jupiter.
  E) the competing gravitational tugs of Mars and Jupiter.

Question 2

The aspect ratio of thickness to width of the galactic disk is about:
 
  A) 1:2.
  B) 1:5.
  C) 1:10.
  D) 1:100.
  E) 1:1,000.

[Moriaki]

Answer to Question 1

D

Answer to Question 2

D

[student77]

TYSM

[emsimon14]

Excellent