$1.$ The refining process that converts low$-$value, high$-$boiling fractions of crude oil into high$-$value, low$-$boiling ones is called $\_\_\_\_\_\_\_\_\_.$

$2.\_\_\_\_\_\_\_\_\_$ is a characteristic property of gasoline.

$3.$ The primary purpose of catalytic reforming is to increase the $\_\_\_\_\_\_\_\_\_$ of gasoline.

$4.$ The refining process used to produce high$-$octane gasoline from low$-$octane naphtha is called $\_\_\_\_\_\_\_\_\_.$