Astronomy current events question: galactic center gamma ray source?

Astronomy 210L, spring semester 2016
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!)

Catherine Zandonella, "Galactic Center's Gamma Rays Unlikely to Originate from Dark Matter, Evidence Shows" (February 4, 2016)
princeton.edu/main/news/archive/S45/34/09S16/index.xml

Statistical analysis of images from NASA's Fermi Gamma-Ray Space Telescope have ruled out __________ as the source of gamma rays from the center of the Milky Way.
(A) random noise.
(B) black holes.
(C) cold hydrogen clouds.
(D) dark matter.
(E) extraterrestrial life forms.

Correct answer: (D)

Student responses
Sections 30678, 30679, 30680
(A) : 4 students
(B) : 4 students
(C) : 5 students
(D) : 26 students
(E) : 2 students