Which of the following explains why archipelago islands are so important to the study of allopatric ...

Which of the following explains why archipelago
  islands are so important to the study of allopatric
  speciation?
  a. All are islands surrounded by water.
  b. They are close to the equatorial continents.
  c. They are distant enough from the continents to
  prevent or impede gene flow.
  d. They prevent genetic isolation by putting all the
  populations into a small area.
  e. They increase genetic drift.

Question 2

Allopatric speciation is most commonly caused by
  a. geographical distance.
  b. the unattractiveness of the females.
  c. a heavy parasite load.
  d. rapid genetic exchange over long distances.
  e. increased genetic drift.