$5.$ Gas burners optimize combustion by adjusting $\_\_\_\_\_,\_\_\_,$ and $\_\_\_\_\_.$

A$)$ air flow, fuel input, ignition timing

B$)$ pipe size, valve pressure, flame color

C$)$ insulation, electric current, water supply

$6.$ Excess air in combustion systems can lead to increased $\_\_\_\_\_,\_\_\_,$ and $\_\_\_\_\_.$

A$)$ heat loss, fuel consumption, emissions

B$)$ efficiency, output, speed

C$)$ pressure, humidity, brightness

$7.$ In thermal cracking, high $\_\_\_\_\_,$ absence of $\_\_\_,$ and $\_\_\_\_\_$ are used to break down hydrocarbons.

A$)$ temperatures, catalysts, pressure

B$)$ pressures, heat, chemical agents

C$)$ humidity, oxygen, carbon dioxide

$8.$ Coal burning in a stoker involves $\_\_\_\_\_,\_\_\_,$ and $\_\_\_\_\_$ for effective combustion.

A$)$ controlled feed, efficient ash removal, good air distribution

B$)$ high speed, low cost, minimal maintenance

C$)$ automatic shutdown, energy storage, rapid cooling