
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Factorize the expression $x^4 + 81$.
A) $(x^2 + 6x + 9)(x^2 - 6x + 9)$  
B) $(x^2 + 2x + 5)(x^2 - 2x + 5)$  
C) $(x^2 + 3x + 4.5)(x^2 - 3x + 4.5)$  
D) $(x^2 + 3x + 9)(x^2 - 3x + 9)$  
E) $(x^2 + 4x + 9)(x^2 - 4x + 9)$

Present the answer in LaTex format: \boxed{Your answer}
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