Astronomy current events question: Earth's oceans from comets?

Astronomy 210L, fall semester 2011
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!)

Charles Q. Choi, "Comets Created Earth's Oceans, Study Concludes," October 5, 2011
http://www.space.com/13185-comets-water-earth-oceans-source.html

The __________ comet Hartley 2 observed by the Herschel Space Observatory may be evidence that Earth's oceans came from comets.
(A) snowflake-like patterns of.
(B) water vapor jets from.
(C) hydrogen isotopes of.
(D) melting polar ice caps on.
(E) plankton and algae growth on.

Correct answer: (C)

Student responses
Sections 70178, 70186, 70200
(A) : 4 students
(B) : 5 students
(C) : 36 students
(D) : 1 student
(E) : 0 students