According to "Fluid Mosaic Model", the quasi-fluid nature of (a) enables the lateral movement of (b) within the bilayer.

Answer

To answer the question based on the "Fluid Mosaic Model", we need to identify the components involved in the lateral movement within the cell membrane. Let's break it down step by step:

### Step-by-Step Solution:

1. **Understanding the Fluid Mosaic Model**:
- The Fluid Mosaic Model describes the structure of cell membranes. It suggests that the membrane is made up of a phospholipid bilayer with embedded proteins that can move laterally within the layer.

2. **Identifying Component A**:
- The question asks about the "quasi-fluid nature of (a)". In the context of the Fluid Mosaic Model, the component that exhibits quasi-fluidity is the **lipids**. Lipids in the bilayer allow for flexibility and movement.

3. **Identifying Component B**:
- The question also asks about the lateral movement of (b) within the bilayer. In this model, the lateral movement primarily refers to the movement of **proteins** that are embedded within the lipid bilayer.

4. **Connecting A and B**:
- The quasi-fluid nature of the lipids (A) enables the lateral movement of proteins (B) within the bilayer. This fluidity allows proteins to move and shift positions, which is essential for various cellular functions.

5. **Final Answer**:
- According to the Fluid Mosaic Model, the quasi-fluid nature of **lipids** (a) enables the lateral movement of **proteins** (b) within the bilayer.

### Summary:
- (a) Lipids
- (b) Proteins