Define and explain the taxonomic category: Class.

In biological nomenclature,which name of an organism,once used,cannot be used for the naming of any other organism?

Which of the following is a class?

$A$ species is taxonomically defined as:

Statement $S$: The family $Columbidae$ includes pigeons and doves,which consist of various genera and species.
Reason $R$: $A$ family is a category formed by a group of closely related genera.
$(a)$ Both $S$ and $R$ are true,and $R$ is the correct explanation of $S$.
$(b)$ Both $S$ and $R$ are true,but $R$ is not the correct explanation of $S$.
$(c)$ $S$ is true and $R$ is false.
$(d)$ $S$ is false and $R$ is true.
$(e)$ Both $S$ and $R$ are false.

$A$ group of closely related species is known as.......