
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
Among the following sampling methods: ① From 15 balls numbered 1 to 15, randomly select 3 as a sample, sort them from smallest to largest, randomly choose a starting point $l$, and then select numbers $l+5$, $l+10$ (if it exceeds 15, start counting from 1 again) for the sample; ② Before products manufactured by a factory are sent to the packaging workshop via a conveyor belt, an inspector checks one product every 5 minutes; ③ In a market survey, it is stipulated to randomly select a person at the entrance of a shopping mall for a survey, until the predetermined number of people has been surveyed; ④ In a cinema audience survey on a certain indicator, it is announced that audience members in every row (with an equal number of people per row) with seat number 12 should stay for a discussion; Among the above sampling methods, the ones that are systematic sampling are (please fill in the corresponding numbers on the line).

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