................ And ..................... Are functional isomers.

Explanation

To identify functional isomers, we need to understand that functional isomers are compounds that have the same molecular formula but differ in the functional groups present in their structures.

### Step-by-Step Solution:

1. **Identify the Molecular Formula**:
Both glucose and fructose have the same molecular formula, which is C6H12O6. This is the first step in confirming that they can be considered isomers.

2. **Determine the Functional Groups**:
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