$21.$ Fractional distillation relies on the principle that different components of crude oil boil at different $\_\_\_\_$; this process is essential for producing $\_\_\_\_$ fuels and $\_\_\_\_$ oils.

$22.$ The ASTM distillation test is crucial for assessing the quality of $\_\_\_\_$ products, providing valuable data for regulatory compliance and $\_\_\_\_$ specification.

$23.$ TBP and EFV distillation methods offer detailed insights into the $\_\_\_\_$ properties of crude oil, guiding the design of $\_\_\_\_$ units and the optimization of $\_\_\_\_$ strategies.

$24.$ Atmospheric distillation units are typically the first stage in crude oil processing, focusing on separating lighter fractions like $\_\_\_\_$ and $\_\_\_\_,$ whereas vacuum distillation units further process the residues to extract $\_\_\_\_$ oils and $\_\_\_\_.$