What are the "rungs" of DNA called?

One of the methods used to reduce energy use is: a. energy efficiency c. energy conservation b. energy reservation d. energy holding select the best answer from the choices provided a b c d i know the answer is not option a

Ascientist and her team counted 200 individual deer in an area of 10 square kilometers. what is the population density?

Which of these substances does not protect against invaders in the nonspecific immune response? a. saliva b. mucus c. tears d. urine