$**$Objective Question $($Chemical Engineering$)$:$**$

How are the principles of fluid$-$solid reactions applied in processes such as catalytic cracking and fluidized bed reactors within chemical engineering?

A$)$ By utilizing catalysts to enhance the rate of chemical reactions between gases and solid surfaces.

B$)$ By maintaining a constant temperature and pressure to optimize reaction kinetics in fluidized bed reactors.

C$)$ By controlling the particle size and distribution to maximize surface area and reactivity in catalytic cracking.

D$)$ By incorporating inert materials to stabilize fluidized beds and prevent particle aggregation.