Astronomy current events question: Martian double-layer craters

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!)

Kevin Stacey, "Big Ice May Explain Mars' Double-Layer Craters," August 5, 2013
http://news.brown.edu/pressreleases/2013/08/craters

Geologists from Brown University developed a possible explanation for double-layered ejecta craters (DLEs) on Mars, which may have been caused by impacts:
(A) into dormant volcanoes.
(B) while its poles were flipping.
(C) that triggered small marsquakes.
(D) of soft binary asteroids.
(E) onto thick glaciers.

Correct answer: (E)

Student responses
Sections 70178, 70186, 70200
(A) : 6 students
(B) : 4 students
(C) : 2 students
(D) : 20 student
(E) : 34 students