What is the structure labeled A?
A. An enzyme
O
B. A substrate
O
O
C. A reactant
D. A product

The structure labeled A is the substrate. The enzyme is the black colored thingy on the bottom.

not: both offer magnification to the atomic level.

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.