The nature of cold weather and excessive urination

A, when it is cold, the cold receptors in the skin are stimulated and the secretion of sweat glands is reduced, so A is wrong;

B, the water in the human body should be balanced, that is, the excretion and intake of water should be balanced, sweat gland secretion is reduced, and other discharge methods are increased, so B is correct;

C, in hot days, sweat gland secretion increases, extracellular fluid osmotic pressure increases, antidiuretic hormone secretion increases, and urine volume decreases, so C is wrong;

D, the sweat gland secretion decreases in cold days, and the osmotic pressure of extracellular fluid decreases, so the urine volume increases, so D is wrong.

Therefore, choose: B.