Video solution:

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Written solution:

To find the number that Yunji left out, we need to find the sum of the integers from $1$ to $9$ and find its difference with the largest perfect square below the sum. We can calculate the sum of the integers from $1$ to $9$ as follows: $$1 + \ldots + 9 = \dfrac{9(9+1)}{2} = 45$$ The largest perfect square less than $45$ would be $36$ and $45 - 36 = 9$.

Thus, E is the correct answer.