
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 events, which are random events (fill in the serial numbers).  
① Tossing a coin twice in succession, and both times it lands heads up;  
② Opposite charges attract each other;  
③ At standard atmospheric pressure, water freezes at 1℃;  
④ Rolling a die and the number facing up is even.

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