3. Variation within a species occurs through a. Mutation
b. sexual reproduction
c. Both mutation and sexual reproduction

4.Which of the following statements is true?

a. Antibiotics kill all bacteria that they encounter

b. Antibiotics don't kill bacteria which have a pre-existing trait allowing them to break

c. Antibiotics don't kill bacteria that evolve an allele allowing them to break down the down the antibiotic antibiotic after they encounter the antibiotic

d. None of these.