
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
The Chronicle of Zuo, in its 14th year of Duke Zhao, records: "If the skin does not exist, where would the hair attach?" This sentence implies that when an object loses the basis for its existence, it cannot exist. Therefore, "having hair" is the ______ condition for "having skin" (fill in the blank with the correct number).
① Sufficient condition
② Necessary condition
③ Necessary and sufficient condition
④ Neither necessary nor sufficient condition

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