Looking at the first 3 terms:
.. 12 -9 = 3
.. 16 -12 = 4 . . . . . 4 ≠ 3, so there is no common difference
12/9 = 4/3
16/12 = 4/3 . . . . . we suspect a common ratio of 4/3
(21 1/3)/16 = 64/48 = 4/3 . . . . the 4th term has the same ratio with the third term
The sequence is geometric with a common ratio of 4/3. The 2nd selection is appropriate.
Note: You have selected the answer with a common ratio that is less than 1. When the common ratio is less than 1, the terms get smaller (closer to zero). That is not the case with this sequence, so you can immediately reject the 3rd selection.