ANS:D - both (b) and (c).

The critical moisture content during the drying of a solid typically increases with increased thickness of the solid and decreased drying rate. Here's why:

1. Increased Thickness of the Solid: When the thickness of the solid increases, the distance that moisture must travel to reach the surface also increases. This results in a longer diffusion path for moisture to migrate from the interior of the solid to the surface for evaporation. As a result, more moisture needs to be absorbed by the solid before it reaches the critical moisture content required for drying to occur. Therefore, an increased thickness of the solid leads to a higher critical moisture content.
2. Decreased Drying Rate: The drying rate is influenced by factors such as temperature, airflow, and humidity. A decreased drying rate means that the rate of moisture removal from the solid is slower. In this scenario, the solid is exposed to drying conditions for a longer period of time before reaching the critical moisture content. As a result, the solid must absorb more moisture before drying can occur, leading to a higher critical moisture content.