Final answer:
The correct answer regarding the function of the gland labeled A is that it increases intestinal calcium absorption (option d), which corresponds to the action of the parathyroid hormone and its role in stimulating vitamin D synthesis and subsequent calcium absorption in the intestine.
Step-by-step explanation:
The client's understanding of endocrine functioning of the gland labeled A would be considered successful if they indicate that it increases intestinal calcium absorption. The gland is likely the parathyroid gland, as parathyroid hormone (PTH) indirectly increases calcium absorption in the small intestine by stimulating the synthesis of vitamin D, which is essential for calcium absorption in the gut. Additionally, the production of calcitriol in the kidney, which is a form of vitamin D, enhances the absorption of Ca2+ from the intestine.
Thus, the correct answer would be "d- Increases intestinal calcium absorption". The other options do not directly relate to the function of the endocrine gland in question: "a- Promotes growth" refers more to growth hormones, "b- Promotes stress response" is associated with adrenal glands producing cortisol, and "c- Increases serum calcium levels" does not specify the mechanism by which calcium levels are increased.