
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 full score of this question is 12 points)  
There are 21 primary schools, 14 middle schools, and 7 universities in a certain area. Now, using stratified sampling, 6 schools are selected from these schools for a vision survey of students.  
(1) Calculate the number of schools that should be selected from primary schools, middle schools, and universities respectively;  
(2) If 2 schools are randomly selected from the 6 selected schools for further data analysis,  
① List all possible outcomes of the selection;  
② Calculate the probability that the 2 selected schools are both primary schools.

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