The correct answer is: B. sand
The permeability of a soil is a measure of how easily water can flow through it. Soils with high permeability, such as sand, allow water to flow through them quickly. Soils with low permeability, such as clay, allow water to flow through them slowly.
Gravel is a type of soil that is made up of large, coarse particles. These particles are too large to pack together tightly, so there are many spaces between them. This allows water to flow through gravel very quickly.
Sand is a type of soil that is made up of smaller particles than gravel. These particles are still too large to pack together tightly, so there are still many spaces between them. This allows water to flow through sand more slowly than through gravel, but still relatively quickly.
Silt is a type of soil that is made up of even smaller particles than sand. These particles are small enough to pack together tightly, so there are fewer spaces between them. This makes it more difficult for water to flow through silt.
Clay is a type of soil that is made up of the smallest particles of all. These particles are so small that they can pack together very tightly, leaving almost no spaces between them. This makes it very difficult for water to flow through clay.
Therefore, the type of soil with a permeability of 0.8 mm/sec is sand.