Simple diffusion/facilitated diffusion requires special membrane proteins.

Explanation

### Step-by-Step Text Solution:

1. **Understanding Passive Transport**: Both simple diffusion and facilitated diffusion are types of passive transport. This means that they do not require energy (ATP) to occur.

2. **Movement Along Concentration Gradient**: In both processes, substances move along the concentration gradient, meaning they move from areas of high concentration to areas of low concentration. This is often referred to as "downhill transport."

3. **Characteristics of Simple Diffusion**:
- Simple diffusion is a slow process.
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