In prehistoric times volcanic eruptions caused mass extinctions of many species of marine organisms attached to the ocean floor. What is the MOST LIKELY reason for this?

Responses
A Volcanic eruptions change the pH and temperature of the ocean.Volcanic eruptions change the pH and temperature of the ocean.
B In prehistoric times, there were very few species of marine organisms.In prehistoric times, there were very few species of marine organisms.
C In prehistoric times, most volcanic eruptions took place on the ocean floor.In prehistoric times, most volcanic eruptions took place on the ocean floor.
D Volcanic eruptions remove all traces of dissolved oxygen in the waters of the oceans.

A Volcanic eruptions change the pH and temperature of the ocean.