Astronomy current events question: Ceres' ocean remnants?

Astronomy 210L, fall 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!)

Elyssia Widjaja, "Dawn Finds Possible Ancient Ocean Remnants at Ceres" (October 26, 2017)
nasa.gov/feature/jpl/dawn-finds-possible-ancient-ocean-remnants-at-ceres

NASA's Dawn spacecraft's observations of __________ indicate that the dwarf planet Ceres may have had an ocean in the past.
(A) released gases.
(B) ongoing volcanic eruptions.
(C) infrared heat sources.
(D) subduction zones.
(E) smooth surface features.

Correct answer: (E)

Student responses
Section 70186
(A) : 5 students
(B) : 2 students
(C) : 3 students
(D) : 4 students
(E) : 7 students