Which of the following are true about the taxonomical aid 'key'?
$(a)$ Keys are based on the similarities and dissimilarities.
$(b)$ Key is analytical in nature.
$(c)$ Keys are based on the contrasting characters in pair called couplet.
$(d)$ Same key can be used for all taxonomic categories.
$(e)$ Each statement in the key is called Lead.
Choose the most appropriate answer from the options given below:

• A
  $(a), (b)$ and $(c)$ only
• B
  $(b), (c)$ and $(d)$ only
• C
  $(a), (b), (c)$ and $(e)$ only
• D
  $(a), (c), (d)$ and $(e)$ only