Which of the following statements are correct?
$(i)$ Drugs that mimic natural messenger by switching on the receptor are called agonists.
$(ii)$ Shape of the receptor does not change after attachment of chemical messenger.
$(iii)$ $A$ cationic detergent is formed when stearic acid reacts with polyethylene glycol.
$(iv)$ Seldane is an antihistamine.

• A
  $(ii)$,$(iii)$
• B
  $(i)$,$(iii)$,$(iv)$
• C
  $(i)$,$(iv)$
• D
  $(i)$,$(ii)$,$(iii)$