
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
Consider the sequence of numbers $\{8, 88, 888, 8888, \ldots, 888888888\}$. Each number is composed of digits that are all 8s, and the number of 8s increases by one in each subsequent number. Calculate the arithmetic mean $N$ of these numbers, and find out which digit is not contained in $N$.
A) 5
B) 6
C) 8
D) None of the above

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