Which of the following is NOT one of the four major intervals in the geologic time scale?

Which of the following is NOT one of the four
  major intervals in the geologic time scale?
  a. Mesozoic
  b. Proterozoic
  c. Carboniferozoic
  d. Cenozoic
  e. Paleozoic

Question 2

The geologic time scale is subdivided on the
  basis of
  a. the appearance of different radioactive
  isotopes in different strata.
  b. levels of background extinction.
  c. periods of mass extinction.
  d. the appearance of different radioactive
  isotopes in different strata and levels of
  background extinction.
  e. the appearance of different radioactive
  isotopes in different strata, levels of
  background extinction, and periods of mass
  extinction.