
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 order to investigate the PM2.5 values in cities, 36 cities are divided into three groups: Group A, Group B, and Group C, with 6, 12, and 18 cities in each group, respectively. If stratified sampling is used to select 12 cities, the number of cities that should be selected from Group B is ▲.

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