
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 medical research institute wanted to understand the effect of a certain serum in preventing colds. They compared the cold records over a year of 500 people who had used the serum with another 500 people who had not used the serum. They proposed the hypothesis H0: "This serum does not have a preventive effect against colds." It is known that by using a 2×2 contingency table, $K^2 \approx 3.918$, and by consulting the critical value table, $P(K^2 \geq 3.841) \approx 0.05$. Among the following conclusions, the correct one is \_\_\_\_\_\_\_\_.

① There is a 95% confidence that "this serum can prevent colds"; ② If a person has not used the serum, then there is a 95% chance that they will catch a cold within a year; ③ The effectiveness of this serum in preventing colds is 95%; ④ The effectiveness of this serum in preventing colds is 5%.

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