The correct option is C Key
Key is a taxonomical aid used for identification of plants and animals based on the similarities and dissimilarities.
Flora is a block containing information of the habitat, climate, seasonal changes, distribution, description and index of plants found in a specific area.
Monograph is treatise having all information about a particular taxon like family or genus.
Manuals are recording descriptions for providing information for identification of names of species found in an area.