Answer:
According to toppr
 Receptors are specific proteins located on target tissues to which specific hormones bind to produce their effect.
 Binding of a hormone to its receptor leads to the formation of a hormone-receptor complex. Formation of Hormone-Receptor complex leads to certain biochemical changes in the target tissue.
 Hence Receptor site responds to a hormone.
 So, the correct answer is 'Receptor'.
Not my own words, I have cited so I am not plagerizing
Explanation: :)