We look for an arithmetic sequence that always increases or decreases by a constant factor of 2 1/2, that is, 2.5.
That means that the result of subtraction of any two consecutive terms of the sequence will always equal 2.5.
Option B) is not correct, because it increases by a constant factor of 2.
Option C) is not correct because it increases by a factor of 1.5
Option D) is not an arithmetic sequence because it does not grow by a constant factor.
The correct option is option A). You can check that the difference of any of its consecutive terms is always equal to 2.5.
8.5 - 6 = 2.5
-1.5 - (- 4) = 2.5
3.5 - 1 = 2.5