Answer:
B. arithmetic sequence; 9
Step-by-step explanation:
An arithmetic sequence is a sequence where there is a common difference between each term. A common difference is a number that is added to the previous term to get the current term. For a sequence to be considered arithmetic this common difference must remain constant. This sequence is arithmetic because each time 9 is added to the previous term to get the next one. So the common difference is 9 and B is correct.
