Astronomy current events question: Chicxulub impact site hydrocarbon soot?

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!)

Kunio Kaiho and Naga Oshima, "Site of Asteroid Impact Changed the History of Life" (November 10, 2017)
tohoku.ac.jp/en/press/asteroid_impact.html

Researchers proposed that the Chicxulub asteroid may not have caused the extinction of dinosaurs if its impact area had been hydrocarbon-poor, based on:
(A) laboratory experiments. (B) fossil carbon dating. (C) analysis of trapped gases. (D) tree ring spacings. (E) computer models.

Correct answer: (E)

Student responses
Sections 70178, 70186
(A) : 7 students
(B) : 7 students
(C) : 17 students
(D) : 0 students
(E) : 7 students