According to Darwin's model of evolution, evolution can only occur if there is some variation present among the individual members of a population. Which statement BEST describes the source of this variation among members of a species?
A Individuals will vary depending on geography and climate.
B Variation exists because not all genes will be expressed.
C Variation among individuals may arise as a result of mutations in the genetic code.
D Variation exists because different individuals will have different access to food and other resources.