The kidneys secrete ADH in response to dehydration.

A. Diuretics increase urine output by inhibiting the reabsorption of water and sodium in the kidneys, which leads to increased water loss. This action is opposite to water conservation, making this the correct answer.

B. The counter current exchange system in the kidneys helps conserve water by maintaining a high osmolarity in the medulla, which facilitates the reabsorption of water in the collecting ducts. This system contributes to water conservation.

C. The collecting duct plays a crucial role in water reabsorption. Antidiuretic hormone (ADH) increases the permeability of the collecting duct to water, allowing more water to be reabsorbed back into the bloodstream, contributing to water conservation.

D. The counter current multiplier is a mechanism in the loop of Henle that creates a concentration gradient in the kidney medulla, which is essential for water reabsorption in the collecting ducts. It contributes to water conservation.

A. Small intestine, particularly the ileum, contains Peyer's patches, which are abundant lymphoid tissues in the mucosa and submucosa. These structures are part of the immune system, protecting the body from pathogens in the digestive tract.

B. Stomach: While the stomach has some lymphoid tissue, it does not have as much as the small intestine, specifically the Peyer's patches.

C. Large intestine has lymphoid nodules, but it does not contain as much lymphoid tissue as the small intestine.

D. Esophagus has very little lymphoid tissue compared to the small intestine, as its primary function is to transport food rather than participate in immune defense.