Astronomy current events question: Ceres' bright spots evaporating?

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!)

Paolo Molaro and Richard Hook, "Unexpected Changes of Bright Spots on Ceres Discovered" (March 16, 2016)
eso.org/public/usa/news/eso1609/

Dwarf planet Ceres' surface spots may be evaporating in sunlight as it rotates, based on European Southern Observatory telescope observations of:
(A) snow avalanches.
(B) cloud formation.
(C) brightness variations.
(D) water vapor geysers.
(E) liquid water reflections.

Correct answer: (C)

Student responses
Sections 30678, 30679, 30680
(A) : 1 student
(B) : 6 students
(C) : 24 students
(D) : 3 students
(E) : 6 students