Astronomy clicker question: isolated white dwarf--nova?

Astronomy 210, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the end of their learning cycle:

An isolated white dwarf cannot explode as a nova because it:
(A) has no companion star to heat up.
(B) expended all of its extra energy during the planetary nebula phase.
(C) has no new source of hydrogen.
(D) does not have enough degeneracy pressure.
(E) (I'm lost, and don't know how to answer this.)

Section 70160
(A) : 15 students
(B) : 2 students
(C) : 10 students
(D) : 0 students
(E) : 0 students
(F) : 0 students

This question was asked again after displaying the tallied results with the lack of consensus, with the following results. No comments were made by the instructor, in order to see if students were going to be able to discuss and determine the correct answer among themselves.

Section 70160
(A) : 9 students
(B) : 0 students
(C) : 19 students
(D) : 0 students
(E) : 0 students
(F) : 0 students

Correct answer: (C)

A white dwarf in a close binary system will take hydrogen from its companion star, and if this mass transfer is sufficiently slow, will undergo a nova explosion. (A rapid mass transfer would result in a type Ia supernova explosion.)

Pre- to post- peer-interaction gains:
pre-interaction correct = 37%
post-interaction correct = 68%
Hake (normalized) gain <g> = 49%