Answer:
b. geometric
Step-by-step explanation:
The terms don't have a common difference, but they do have a common ratio: 2. A sequence in which terms have a common ratio is a geometric sequence.
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Differences are ...
2/3 -1/3 = 1/3
4/3 -2/3 = 2/3 . . . . not the same
Ratios are ...
(2/3)/(1/3) = 2
(4/3)/(2/3) = 2
(8/3)/(4/3) = 2 . . . . ratios are common between pairs of terms
