Which of the following rock types form when silt that was deposited in a river hardens into a solid mass?AsedimentaryBextrusiveCigneousDmetamorphic

The rock type that forms when silt that was deposited in a river hardens into a solid mass is sedimentary. Here's why:

1. Sedimentary rocks are formed from the accumulation of sediments. These sediments can be small particles of rocks, minerals, or the remains of plants and animals. When these sediments are deposited over time, they can harden into a solid mass, forming sedimentary rocks.

2. In the context of the question, silt is a type of sediment. When silt is deposited in a river and hardens over time, it forms a sedimentary rock.

3. The other options - extrusive, igneous, and metamorphic rocks - are formed through different processes. Extrusive rocks are formed when magma cools and solidifies on the Earth's surface. Igneous rocks are formed from the solidification of magma or lava. Metamorphic rocks are formed when existing rocks are subjected to high temperatures and pressures, causing them to change physically or chemically.

So, the answer is A. Sedimentary.