PLEASE HELP!! BIOLOGY Which of the following is NOT an element in the process of natural selection?

a
Individuals struggle for survival.
b
Organisms cause environmental change.
c
Fitness with your environment can lead to an increase in your population.
d
Genetic variation exists within a species.

What do isotopes of uranium have the same number of? what do they have a different number of? a) same number of protons; different number of electrons b) same number of protons; different number of neutrons c) same number of electrons; different number of protons d) same number of neutrons; different number of protons