Assertion (A): The person with diabetes insipidus feels thirsty. Reason (R): A person with diabetes insipidus suffers from excess secretion of vasopressin.

1. Assertion (A) is true. Diabetes insipidus is a condition characterized by the kidneys being unable to conserve water, leading to excessive urination (polyuria) and consequently, intense thirst (polydipsia). 2. Reason (R) is false. Diabetes insipidus is typically caused by a deficiency in the secretion or action of the antidiuretic hormone (vasopressin), not an *excess* secretion. Lack of vasopressin leads to the kidneys excreting large amounts of dilute urine. 3. Since A is true and R is false, the correct option is (C).