In a lipid bilayer, ……..... of lipid molecules are sandwiched between ....

Options

A. hydrophobic heads, hydrophilic tails
B. hydrophobic tails, hydrophilic heads
C. hydrophilic heads, hydrophilic tails
D. hydrophobic tails, hydrophobic heads

Explanation

### Step-by-Step Solution:

1. **Understanding the Structure of the Cell Membrane**:
- The cell membrane is primarily composed of a lipid bilayer, which serves as a barrier between the internal environment of the cell and the external environment.

2. **Identifying the Components of the Lipid Bilayer**:
- The main component of the lipid bilayer is phospholipids. Each phospholipid molecule has a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails.

3. **Describing the Arrangement of Phospholipids**:
- In the lipid bilayer, the hydrophobic tails of the phospholipids face inward, away from water, while the hydrophilic heads face outward towards the aqueous environments both inside and outside the cell.

4. **Formulating the Answer**:
- Therefore, in a lipid bilayer, the **hydrophobic tails** of lipid molecules are sandwiched between the **hydrophilic heads**.

5. **Final Answer**:
- The correct completion of the statement is: "In a lipid bilayer, **hydrophobic tails** of lipid molecules are sandwiched between **hydrophilic heads**."