Which of the following is a run-on sentence?
A. Her eyes were shining brilliantly. Her face had lost its color within twenty seconds.
B. Her eyes were shining brilliantly, her face had lost its color within twenty seconds.
C. Her eyes were shining brilliantly; her face had lost its color within twenty seconds.
D. Her eyes were shining brilliantly, but her face had lost its color within twenty seconds.
