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.

sexual reproduction produces offspring with novel combinations of genes. species that reproduce sexually must maintain two different types of individuals, males and females, which can limit the ability to colonize new habitats as both sexes must be present.

d.

hope to be marked brainliest