Astronomy current events question: white dwarfs polluted by asteroid-like infall

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!)

NASA press release, "NASA's Hubble Space Telescope Finds Dead Stars Polluted with Planet Debris," May 9, 2013
http://www.nasa.gov/mission_pages/hubble/science/hyades-dwarf.html

NASA's Hubble Space Telescope observed __________, which may be evidence that white dwarfs are being polluted by asteroid-like debris falling onto them:
(A) silicon and carbon in white dwarfs' atmospheres.
(B) numerous transits across white dwarfs.
(C) decreasing white dwarf fusion rates.
(D) strong wobbles in white dwarf positions.
(E) increasing white dwarf masses.

Correct answer: (A)

Student responses
Sections 30682
(A) : 11 students
(B) : 4 students
(C) : 1 student
(D) : 1 student
(E) : 5 students