A diploid somatic cell from a rat has a total of 42 chromosomes. What is the total number of DNA molecules present in the cell during prophase I of meiosis I? a. 21.
b. 42.
c. 84.
d. 168.

Why might surface mining be less risky for miners than underground mining? a. surface miners can become trapped in a collapsed mine. b. surface miners work in dusty, enclosed areas. c. surface miners work aboveground. d. surface miners use elevators to enter mines.

In the context of the neural impulse, which of the following is true about the depolarization of neuron membranes?

Which conditions are necessary for natural selection to occur? select all of the answers that apply. a. inheritable adaptations vary among individuals. b. the population size is increasing. c. more individuals are born than can survive. d. fitness varies among individuals. e. the environment changes suddenly and drastically.