**Core Concept**
Hyperparathyroidism (high PTH levels) is a condition where the parathyroid glands produce excess parathyroid hormone (PTH), leading to an increase in plasma calcium levels. To counteract this, the body employs mechanisms to reduce plasma calcium levels and restore balance.

**Why the Correct Answer is Right**
To decrease plasma calcium levels, PTH stimulates the kidneys to increase phosphate excretion and activate the enzyme 1-alpha-hydroxylase, which converts 25-hydroxyvitamin D to its active form, 1,25-dihydroxyvitamin D (calcitriol). Calcitriol then enhances calcium absorption from the gut, reduces calcium reabsorption in the kidneys, and promotes bone resorption, ultimately lowering plasma calcium levels.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might seem plausible, but the correct answer is not about increasing calcium excretion in the urine. Instead, it's about the complex interplay of mechanisms to lower plasma calcium levels.
**Option B:** Although PTH does affect bone resorption, this option is incomplete and doesn't address the primary mechanisms involved in reducing plasma calcium levels.
**Option C:** The renin-angiotensin-aldosterone system (RAAS) primarily regulates blood pressure and electrolyte balance, but it's not directly involved in the body's response to high PTH levels.

**Clinical Pearl / High-Yield Fact**
The body's ability to lower plasma calcium levels in response to high PTH levels is a classic example of a negative feedback loop, where the excess hormone (PTH) triggers a cascade of events to counteract its effects.

**Correct Answer:** C.