The two correct choices are:
B. Igneous rock can only form after rock has melted to become magma.
C. Sedimentary rocks can form from both sediments of igneous and metamorphic rock.
Igneous rocks are formed through the cooling and solidification of molten rock material, either magma (below the Earth's surface) or lava (on the Earth's surface). This process is called crystallization. So, for igneous rocks to form, there must be a phase where rock material undergoes melting to become magma.
Sedimentary rocks are formed through the accumulation and cementation of sediments. These sediments can be derived from the weathering and erosion of pre-existing rocks, which can include both igneous and metamorphic rocks. Over time, these sediments can be compacted and cemented together to form sedimentary rocks.