Astronomy current events question: Vesta hydrated minerals

Astronomy 210L, fall semester 2012
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!)

Jia-Rui Cook, Dwayne Brown, "Dawn Sees Hydrated Minerals on Giant Asteroid," September 20, 2012
http://www.nasa.gov/mission_pages/dawn/news/dawn20120920.html

NASA's Dawn spacecraft has revealed the presence of hydrogen-bearing compounds on the equator of the giant asteroid Vesta, which may have come from:
(A) the natural radioactivity of surface compounds.
(B) lava-like flows of ancient glaciers.
(C) contamination from propellant used by the Dawn spacecraft.
(D) pockets of methane released during its early formation.
(E) impacts that had brought and vaporized water-bearing compounds.

Correct answer: (E)

Student responses
Sections 70178, 70186, 70200
(A) : 4 students
(B) : 4 students
(C) : 3 students
(D) : 3 students
(E) : 38 students