What substance makes up most of earth's crust
a. soil
b. sediment
c. rock
d. sand

Rocks are the substance that makes up most of earth's crust. The correct option in regards to the given question is option "C". Silicon is present in large amounts in sands. With silicon, oxygen is also present in the earths crust.The silicate materials like quartz and feldspar are also present. Large rocks are definitely present along with the magma that is present. It can be seen that with the magma, rocks also come out when volcanic eruptions occur. although silicon is also present in the earths crust, but they are never in the form of sand.