(A)
Increased calories may result in weight gain, but there is no indication in this question that this man's diet has changed in a way that would result in increased calories. (B) Decreasing cardiac output stimulates the renin-angiotensin-aldosterone cycle and results in fluid retention, which is reflected by weight gain. (C) Decreasing renal function may result in fluid retention, but this question gives no indication that this man has any renal problems.
(D)
Profound diuresis occurs with diabetes insipidus, which results in weight loss.