Based on the provided options relating to the rock cycle, the true statement is:
**D. All three types of rock can be weathered to form sediment.**
Here's a brief explanation for each option:
A. **Only sedimentary rock can undergo heat and pressure to form metamorphic rock.** - This is false because both igneous and sedimentary rocks can undergo metamorphism.
B. **All three types of rock can be formed when magma cools.** - This is false because only igneous rock is formed from cooling magma. Sedimentary and metamorphic rocks are formed through different processes.
C. **Only metamorphic rock can be melted to form magma.** - This is false because both igneous and sedimentary rocks can also be melted to form magma.
D. **All three types of rock can be weathered to form sediment.** - This statement is true because igneous, sedimentary, and metamorphic rocks can all be broken down into sediment through weathering processes.