Astronomy current events question: North American nebula young stars

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!)

Whitney Clavin, "New View of Family Life in the North American Nebula," February 10, 2011
http://www.jpl.nasa.gov/news/news.cfm?release=2011-047

NASA's Spitzer Space Telescope was able to identify 2,000 previously unknown young stars in the North American nebula by:
(A) observing when they are eclipsed by their planets.
(B) triangulating regions of collapsing gas and dust.
(C) accidentally running out of liquid coolant.
(D) detecting their infrared glow.
(E) recovering back-up data from a software crash.

Correct answer: (D)

Student responses
Sections 30678, 30679, 30680
(A) : 1 student
(B) : 16 students
(C) : 0 students
(D) : 31 students
(E) : 0 students