Astronomy current events question: Mercury surface composition

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!)

Kelly Beatty, "Mercury Shows Its True Colors," October 3, 2011
http://www.skyandtelescope.com/news/home/131009713.html

NASA's Messenger spacecraft has measured the amounts of radioactive potassium, thorium, and uranium in Mercury's crust by __________ from orbit.
(A) detecting gamma rays.
(B) analyzing Mercury's ring particles.
(C) transmitting/receiving radar pulses.
(D) comparing reflectivity of different regions.
(E) recording infrared thermal emissions.

Correct answer: (A)

Student responses
Sections 70178, 70186, 70200
(A) : 19 students
(B) : 3 students
(C) : 2 students
(D) : 0 students
(E) : 7 students