**Core Concept**
Cancer cells exhibit altered metabolism, often referred to as the Warburg effect, where they preferentially use glycolysis for energy production even in the presence of sufficient oxygen. This leads to increased glucose uptake and lactate production. The primary source of nutrition for cancer cells is glucose.

**Why the Correct Answer is Right**
Cancer cells have an increased expression of glucose transporter 1 (GLUT1) on their surface, allowing for enhanced glucose uptake. The enzyme hexokinase is also overexpressed, facilitating the conversion of glucose to glucose-6-phosphate. This shift in metabolism supports the rapid growth and proliferation of cancer cells. The increased lactate production is due to the inhibition of pyruvate dehydrogenase, the enzyme responsible for converting pyruvate to acetyl-CoA for oxidative phosphorylation.

**Why Each Wrong Option is Incorrect**
**Option A:** Although cancer cells do require amino acids for protein synthesis, this is not their primary source of nutrition.
**Option B:** Cancer cells do not primarily derive nutrition from fatty acids, despite their increased lipid metabolism.
**Option C:** Although cancer cells can use glycerol for energy production, this is not their primary source of nutrition.

**Clinical Pearl / High-Yield Fact**
The Warburg effect is a hallmark of cancer metabolism, and targeting this metabolic shift is a promising therapeutic strategy for cancer treatment.

**Correct Answer: A. Glucose.**