The correct option is
B Thymus - thymosin - proliferation of T-lymphocytes
A. Oxytocin is secreted from the posterior pituitary and helps in the contraction of uterus during childbirth and also stimulates release of milk from mammary glands i.e. lactation.
B. Vasopressin or Anti diuretic hormone (ADH), is secreted from the posterior part of pituitary gland. This hormone increases reabsorption of water in kidneys and this results in decreased rate of urine production.
C. Thymus gland is associated with the development of immune system and present on the dorsal side of heart. It secretes thymosin hormone which plays an important role in the differentiation of T-lymphocytes.
D. Glucagon is secreted from αα-cells of islets of Langerhans of pancreas. It increases blood sugar level by stimulating glycogenolysis (i.e. break down of glucose) and gluconeogenesis (synthesis of glucose).
Hence, option C is the correct combination for gland, hormone and its function.
So, the correct answer is 'Thymus - thymosin - proliferation of T-lymphocytes'.