The correct option is D Flora
Flora, manuals, monographs and catalogues are some other means to help in correct identification.
Flora contains the actual account of habitat and distribution of plants of a given area. These provide the index to the plant species found in a particular area.
Manuals are useful in providing information for identification of names of species found in an area.
Monographs contain information of any one taxon.
Catalogue is simply a listing of all species organized in an order. These are usually in alphabetical order.