Astronomy current events question: water flowing on Mars?

Astronomy 210L, Spring 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!)

Kelly Beatty, "Is Water Flowing on Mars?," March 11, 2011
http://www.skyandtelescope.com/news/home/117806243.html

__________ observed by NASA's Mars Global Surveyor may be evidence of water flowing on Mars.
(A) Shifting positions of boulders and other rock debris.
(B) Wearing down of angular rock formations.
(C) Light reflected by rocks exposed by meteor impacts.
(D) The appearance, growth, and fading of dark rivulets.
(E) Accumulation of ice in shadowed north and south pole craters.

Correct answer: (D)

Student responses
Sections 30678, 30679, 30680
(A) : 3 students
(B) : 9 students
(C) : 1 student
(D) : 20 students
(E) : 16 students