
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
**Text**: Among the following sampling methods, which ones are systematic sampling? Fill in the sequence number.  
① From 15 balls numbered 1 to 15, randomly select 3 as a sample, sort them from the smallest number to the largest, randomly choose a starting point $i_0$, and then sample the balls numbered $i_0 + 5$, $i_0 + 10$ (if it exceeds 15, start counting from 1 again);  
② Before the products produced by a factory are sent to the packaging workshop via a conveyor belt, an inspector samples one product from the conveyor belt every five minutes for inspection;  
③ For a certain market survey, it is stipulated to randomly select a person at the entrance of a shopping mall for an interview, until the predetermined number of interviewees is reached;  
④ For a survey on a certain indicator among moviegoers, it is arranged for the audience sitting in the seat number 14 of each row (each row has an equal number of seats) to stay for a discussion.

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