**Core Concept**
The question is testing the student's knowledge of hormones that regulate blood glucose levels. Glucose homeostasis is maintained by a balance between hormones that increase and decrease blood glucose levels. The hormones that increase blood glucose levels are primarily glucagon, cortisol, and growth hormone, which stimulate glycogenolysis and gluconeogenesis.

**Why the Correct Answer is Right**
Glucagon is a hormone secreted by the pancreas that increases blood glucose levels by stimulating glycogenolysis in the liver and gluconeogenesis in the liver and kidneys. Cortisol is a hormone secreted by the adrenal gland that increases blood glucose levels by stimulating gluconeogenesis and inhibiting glucose uptake in peripheral tissues. Growth hormone is a hormone secreted by the pituitary gland that increases blood glucose levels by stimulating gluconeogenesis and inhibiting glucose uptake in peripheral tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, so we cannot evaluate it.
**Option B:** This option is not provided, so we cannot evaluate it.
**Option C:** This option is not provided, so we cannot evaluate it.

**Clinical Pearl / High-Yield Fact**
The hormones that decrease blood glucose levels are insulin, which stimulates glucose uptake in peripheral tissues, and amylin, which inhibits gastric emptying and reduces glucagon secretion.

**Correct Answer: A. Insulin**