
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
In the spatial quadrilateral $OABC$, $\overrightarrow{OA}=a$, $\overrightarrow{OB}=b$, $\overrightarrow{OC}=c$. Point $M$ is on $OA$ with $OM=2MA$, and $N$ is the midpoint of $BC$. Among the following vectors, the one parallel to $\overrightarrow{MN}$ is __________ (only fill in the corresponding number).

$① 3a-4b+3c$；$② -4a+3b+3c$；$③ 3a+3b-4c$；$④ \dfrac{4}{3}a-b-c$．

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