Astronomy quiz question: only portion of Milky Way visible

Astronomy 210 Quiz 6, spring semester 2012
Cuesta College, San Luis Obispo, CA

Only a small portion of the Milky Way disk is visible to the naked eye because of:
(A) the finite speed of light.
(B) dark matter.
(C) interstellar gas and dust.
(D) expanding space.

Correct answer: (C)

Section 30674
Exam code: quiz06niLl
(A) : 1 student
(B) : 3 students
(C) : 28 students
(D) : 1 student

"Success level": 86% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33

Section 30676
Exam code: quiz06suE7
(A) : 1 student
(B) : 5 students
(C) : 26 students
(D) : 3 students

"Success level": 76% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.56