At the End of the Permian Era 250 Million Years

At the end of the Permian era 250 million years ago, 80% of all species living on land and 90% of all species living in the oceans disappeared. Which of these is among the MOST plausible explanations for this massive extinction?

A) global warming from volcanic gases released during the breakup of the Gondwanaland supercontinent
B) nearby supernova (the explosion and total destruction of a star)
C) devastating impact by an asteroid
D) "snowball Earth" episode in which global cooling caused Earth's ocean surfaces to freeze and glaciers to cover the continents