**Core Concept**
Vitamin D intoxication occurs when excessive amounts of vitamin D are ingested, leading to an overproduction of calcitriol (1,25-dihydroxyvitamin D), the active form of vitamin D. This results in increased absorption of calcium from the intestine, which can cause hypercalcemia.

**Why the Correct Answer is Right**
Vitamin D intoxication is characterized by features such as hypercalcemia, which can lead to symptoms like nausea, vomiting, and abdominal pain. Additionally, it can cause increased levels of calcium in the urine, resulting in kidney stones. The increased calcium levels can also affect the heart, leading to cardiac arrhythmias and hypertension. Furthermore, vitamin D intoxication can cause changes in the bone, leading to bone resorption and osteoporosis.

**Why Each Wrong Option is Incorrect**
**Option A:** While hypercalcemia is a feature of vitamin D intoxication, decreased calcium levels are not typically associated with this condition. Vitamin D intoxication leads to increased absorption of calcium from the intestine, not decreased.
**Option B:** Nausea and vomiting are indeed features of vitamin D intoxication, particularly due to the hypercalcemia associated with this condition.
**Option C:** Kidney stones are a potential complication of vitamin D intoxication due to the increased levels of calcium in the urine.
**Option D:** While hypertension is a potential complication of vitamin D intoxication, it is not a direct feature of this condition.

**Clinical Pearl / High-Yield Fact**
Vitamin D intoxication can be caused by excessive intake of vitamin D supplements, which can be seen in patients taking high doses of vitamin D for osteoporosis or other conditions.

**Correct Answer: A. Decreased calcium levels.**