$9.$ Thermal cracking is essential for breaking down complex hydrocarbons without a $\_\_\_\_\_,$ using high $\_\_\_,$ and under controlled $\_\_\_\_\_$ conditions.

A$)$ catalyst, temperatures, pressure

B$)$ solvent, electricity, thermal

C$)$ filter, chemical reagents, atmospheric

$10.$ The principle of using excess air in combustion systems is to ensure complete $\_\_\_\_\_,$ although it can lead to increased $\_\_\_,$ and higher $\_\_\_\_\_.$

A$)$ combustion, heat loss, fuel costs

B$)$ pressure, energy efficiency, speed

C$)$ moisture, temperature stability, operational noise

$11.\_\_\_\_\_$ emissions are a significant concern in oil burners, which can be mitigated by optimizing $\_\_\_,$ and maintaining proper $\_\_\_\_\_.$

A$)$ CO$2,$ air$-$to$-$fuel ratio, combustion temperatures

B$)$ NOx, pressure levels, flame color

C$)$ SO$2,$ fuel quality, pipeline integrity

$12.\_\_\_\_\_$ is used in oil refining to increase the octane rating of gasoline, which involves the re$-$structuring of molecules under $\_\_\_$ and with the aid of a $\_\_\_\_\_.$

A$)$ Catalytic cracking, high pressure, catalyst

B$)$ Catalytic reforming, moderate heat, chemical additive

C$)$ Isomerization, controlled conditions, catalyst