The diagram below shows the basic materials and processes involved in the rock cycle.

Based on the information provided about the rock cycle, the true statement is:

A. **All three types of rock can be weathered to form sediment.**

Explanation:
- Igneous, sedimentary, and metamorphic rocks can all undergo weathering and erosion, leading to the formation of sediment.
- Sedimentary rock can undergo heat and pressure to form metamorphic rock, but other types of rock can also be transformed through various processes, including melting.
- All three rock types do not form from cooling magma; only igneous rock forms directly from cooling magma.
- Metamorphic rock can be melted to form magma, but igneous and sedimentary rocks can also undergo processes that lead to melting.

Therefore, "All three types of rock can be weathered to form sediment" is the accurate statement.