4) B

Always remember that when water needs to be kept in the body, the urine produced will be concentrated. This eliminates A, C and F.

Since, water needs to be kept in the body, more water must be reabsorbed from the nephrons. In order to reabsorb more water, ADH production must increase. This is shown only by B.
ADH (Anti-Dieuretic Hormone) reabsorbs water from kidney.