Animals without backbones are called
a. arthropods
c. invertebrates
b. chordates
d. vertebrates

invertebrates

Explanation:

The invertebrates lack a backbone. They include molluscs, annelida, arthropods and protozoa. They have a segmented body and well developed digestive system. Some are mostly found in sea, land or deserts. Some invertebrates lack a rigid exoskeleton. Some are pseudocoelum, possessing cavity between body wall. Some invertebrates have an incomplete digestive system consists of a digestive cavity with one opening which serves as both mouth and anus. Some invertebrates have a complex nervous system consisting of brain and several other sense organs.

the rocks are classified by the geological process they are formed by. the three main groups of rocks are igneous, metamorphic, and sedimentary. minerals are not they are classified under the chemical classes they are in. these groups include silicates, sulfates and carbonates.