
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
A high school has $21$ classes in grade one, $14$ classes in grade two, and $7$ classes in grade three. Using stratified sampling, $6$ classes are selected from these classes for a vision test. If $2$ classes are randomly selected from these $6$ classes for further data analysis, find the probability that both classes are from grade one.

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