Ans: A
Let $d$ be the common difference of the arithmetic sequence.
Let $d$ be the common difference of the arithmetic sequence.
Note that the first $7$ terms of the sequence are $a$, $a + d$, $\ldots$, $a + 6d$.
Note also that the last $7$ terms of the sequence are $a + 42d$, $a + 43d$, $\ldots$, $a + 48d$.
It is obvious that $42d$ is added to each number of the first set of numbers to become the second set of numbers.
Note that $42d$ is a constant. Then a constant is added to each data of the first set of numbers to become the second set of numbers.
Therefore, the variance remains unchanged. i.e. the required variance is $9$.
