The correct answer is: C. Metamorphic rocks.
Fire clay is a type of clay that is found in metamorphic rocks. It is a very fine-grained clay that is high in kaolinite, a type of mineral that is resistant to heat. Fire clay is used in the manufacture of ceramics, bricks, and other products that need to withstand high temperatures.
Igneous rocks are formed when molten rock cools and solidifies. Sedimentary rocks are formed when layers of sediment, such as sand, mud, and gravel, are compacted and cemented together. Soil is a mixture of minerals, organic matter, water, and air.
Igneous rocks are not a good source of fire clay because they are not fine-grained and do not contain kaolinite. Sedimentary rocks are also not a good source of fire clay because they are not as resistant to heat as metamorphic rocks. Soil is not a good source of fire clay because it is too coarse-grained and contains too much organic matter.
Metamorphic rocks are the best source of fire clay because they are fine-grained, contain kaolinite, and are resistant to heat.