Question: Some types of bacteria can only live where oxygen is not present. These bacteria were well adapted to life on Earth over 2 billion years ago. Which of the following changes caused many of these bacteria to become extinct?

  Options: 
 A. the slow movement of tectonic plates
 B. the varying temperatures of each season
 C. an increase in volcanic activity under the oceans
 D. an increase in the number of photosynthetic organisms
Answer: D