Astronomy current events question: 'black rain' on Callisto and Ganymede

Astronomy 210L, spring semester 2013
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Kelly Beatty, "'Black Rain' on Callisto and Ganymede," February 20, 2013
http://www.skyandtelescope.com/community/skyblog/newsblog/Black-Rain-on-Callisto-and-Ganymede-192179541.html

Researchers led by the Southwest Research Institute proposed that particles from Jupiter's outer moons darkened the surfaces of Jupiter's two big inner moons, based on:
(A) measuring radioactivity levels.
(B) studying similar features on Earth's moon.
(C) telescope observations of debris clouds.
(D) analysis of material scooped from Jupiter's moons.
(E) computer simulations and calculations.

Correct answer: (E)

Student responses
Sections 30678, 30679, 30680
(A) : 6 students
(B) : 2 students
(C) : 30 students
(D) : 7 students
(E) : 10 students