
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
Among the following statements, the correct one is (fill in the serial number).  
① A geometric body that has one polygonal face and all other faces are triangles is a pyramid;  
② Cutting a pyramid with a plane, the geometric body formed between the base and the cutting plane is called a frustum;  
③ Any face of a triangular pyramid can be considered as the base.

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