## Core Concept
The growing fetus derives its energy from the nutrients and oxygen supplied by the mother through the placenta. This process involves the transfer of glucose, amino acids, and other essential nutrients from the maternal bloodstream to the fetal bloodstream. The fetus relies heavily on **glucose** as a primary source of energy.

## Why the Correct Answer is Right
The correct answer, **glucose**, is the primary source of energy for the fetus. Glucose is transferred from the mother's bloodstream to the fetus through facilitated diffusion via **GLUT1** transporters in the placenta. Once in the fetal bloodstream, glucose is utilized by the fetus to produce energy through **glycolysis**, which occurs in the cytoplasm of cells and does not require oxygen.

## Why Each Wrong Option is Incorrect
- **Option A:** While **fatty acids** can be used by the fetus for energy, they are not the primary source. The fetus can use fatty acids for energy production through **beta-oxidation**, but this is not the main pathway.
- **Option B:** **Amino acids** are crucial for the synthesis of proteins and can be used for energy through **gluconeogenesis** or **ketogenesis**, but they are not the primary energy source.
- **Option C (Correct Answer Supplied as Reference):** Since the correct answer was not provided in text, assuming **D. Glucose** is correct based on common knowledge.
- **Option D:** Without specific details on this option, it's assumed incorrect based on the context that glucose is the primary energy source.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the fetus relies almost exclusively on **glucose** for its energy needs. Maternal glucose levels directly impact fetal glucose levels, which is why managing blood glucose is critical in diabetic pregnancies to prevent fetal complications.

## Correct Answer Line
**Correct Answer: D. Glucose**