$13.$ The main challenge in the combustion of low$-$grade fuels is to achieve high $\_\_\_\_\_,$ while controlling $\_\_\_,$ and minimizing $\_\_\_\_\_.$

A$)$ efficiency, costs, energy consumption

B$)$ speed, heat, pressure

C$)$ heat output, emissions, ash content

$14.\_\_\_\_\_$ control technologies are essential in managing emissions from stokers, which include $\_\_\_,\_\_\_,$ and $\_\_\_\_\_.$

A$)$ Emission, scrubbers, precipitators, filters

B$)$ Combustion, regulators, moderators, stabilizers

C$)$ Efficiency, sensors$,$ actuators, controllers

$15.$ The efficiency of an oil burner can be assessed by measuring $\_\_\_\_\_,\_\_\_,$ and $\_\_\_\_\_.$

A$)$ fuel usage, heat output, emission levels

B$)$ noise, heat loss, oil viscosity

C$)$ color, texture, viscosity

$16.$ The API gravity of crude oil affects its $\_\_\_\_\_,\_\_\_,$ and $\_\_\_\_\_$ in the refining process.

A$)$ market value, processing difficulty, yield of light distillates

B$)$ color, taste, odor

C$)$ solidity, opacity, weight