What is the taxonomic rank of $Rhizobium$?

The naming and classification of living organisms are based on what?

Give a scientific reason: Classification is essential for understanding the inter-relation among living organisms.

........... is the genus of man.

Assertion $(S)$: Carolus Linnaeus is known as the father of taxonomy.
Reason $(R)$: Linnaeus proposed the binomial nomenclature system and conducted extensive studies in classification.
$(A)$ 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.

The basic unit of classification for plants and animals is ....