What are petroleum fractionation? (Multiple Choice)

What are petroleum fractionation?
 
  a. By heating the crude within preestablished temperature ranges, the vapors of the constituent compounds formed then are condensed and collected within separate receivers.
  b. By cooling the crude within preestablished temperature ranges, the vapors of the constituent compounds formed then are condensed and collected within separate receivers.
  c. Constituent compounds are separated by adding chemical fractions.
  d. The separating of compounds from the original material through mathematically identifying their densities and then allowing them to settle.