What allows each strand of DNA to serve as a template for a new DNA strand during replication?

What allows each strand of DNA to serve as a template for a new DNA strand during replication?
  a. covalent bonding between nucleotide bases
  b. hydrogen bonds between the deoxyribose and the phosphate groups
  c. complementary base pairing between purines and purines on opposite strands
  d. complementary base pairing between pyrimidines and pyrimidines on opposite strands
  e. complementary base pairing between purines and pyrimidines on opposite strands

Question 2

Individuals with mutations in excision repair enzymes may suffer from ____ due to unrepaired DNA damage caused
  by ____.
  a. skin cancer; mutations inherited from their parents
  b. colon cancer; the passing of DNA mutations to daughter cells
  c. prostate cancer; telomerase
  d. skin cancer; the suns UV rays
  e. skin cancer; complementary base pairing