$A$ student of taxonomy was puzzled when told by his professor to look for a key to identify a plant. He went to his friend to clarify what 'Key' the professor was referring to? What would the friend explain to him?

• A
  $A$ physical key to unlock a cabinet containing plant specimens.
• B
  $A$ taxonomic key used for the identification of organisms based on contrasting characters.
• C
  $A$ digital password to access a botanical database.
• D
  $A$ secret code used to label herbarium sheets.