To find the common difference, we subtract consecutive terms in the sequence.
a6 = an + 5
We are given a6 = a1 + 5, so we can substitute this in:
a1 + 5 = a1 + 5
Notice that a1 cancels out on both sides.
5 = 5
Since this equation is true, we know that a1 = a6 + 5 holds for any value of a1.
Therefore, the common difference is 5.
Answer: C. 5