Astronomy current events question: pending eruption on Io?

Astronomy 210L, fall semester 2019
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!)

Julie Rathbun, Anita Heward, Livia Giacomini, Adriana Postiglione, Alan Fischer, "Is Huge Volcano on Jupiter's Moon Io About to Erupt this Month?" (September 17, 2019)
europlanet-society.org/is-huge-volcano-on-jupiters-moon-io-about-to-erupt-this-month/

Loki, the largest volcano on Jupiter's moon, Io, is expected to erupt soon, based on:
(A) sulfur plumes.
(B) collapsing plains.
(C) massive ioquakes.
(D) eruption cycle timing.
(E) magnetic field strengths.

Correct answer: (D)

Student responses
Sections 70178, 70186
(A) : 4 students
(B) : 3 students
(C) : 2 students
(D) : 18 students
(E) : 9 students