What evidence suggests that the populations of paramecia affect each other

Decrease in number.

Explanation:

Decrease in number is the evidence that shows that the populations of paramecia affect each other because the food is limited in the environment and the paramecia species compete for the food source. During this competition, the population of paramecia decreases and only those species survive which avail the food while the remaining will die due to unavailability of food.

the answer to your question is:

c. complementary base-pairing