Astronomy current events question: asteroid 3200 Phaeton a "rock comet?"

Astronomy 210L, fall 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!)

Europlanet Media Centre, "Phaethon Confirmed as Rock Comet by STEREO Vision," September 10, 2013
http://www.sciencedaily.com/releases/2013/09/130910093915.htm

Evidence that asteroid 3200 Phaeton may be a "rock comet" is/are observations of its __________ by NASA's STEREO A spacecraft.
(A) dust particle tail.
(B) internal core heat.
(C) high density.
(D) reflective ice crust.
(E) miniature polar caps.

Correct answer: (A)

Student responses
Sections 70178, 70186, 70200
(A) : 51 students
(B) : 5 students
(C) : 3 students
(D) : 1 student
(E) : 1 student