
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
In a certain urban area, there are a total of 2,000 households, including 1,800 farmer households, 100 worker households, and the rest are intellectual households. Now, a sample of 40 households is to be drawn to investigate the family income situation. The sampling methods that can be used in the entire sampling process are ______. (Fill in the serial number)  
① Simple random sampling; ② Systematic sampling; ③ Stratified sampling.

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