Astronomy current events question: habitability of "garnet" plants

Astronomy 210L, spring semester 2017
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!)

Johana Teske, Cayman Unterborn, Wendy Panero, Karen Masters, and Jordan Raddick, "Between a Rock and a Hard Place: Can Garnet Planets Be Habitable?" (January 5, 2017)
sdss.org/press-releases/between-a-rock-and-a-hard-place-can-garnet-planets-be-habitable/

Computer simulations using star composition data indicate that some "Earth-like" planets may have minerals unsuitable for:
(A) active volcanoes.
(B) oceans.
(C) sustaining magnetic fields.
(D) tectonic plate motion.
(E) commercial mining.

Correct answer: (C) or (D)

Student responses
Sections 30679, 30680
(A) : 3 students
(B) : 12 students
(C) : 11 students
(D) : 13 students
(E) : 1 student