Which sequences are geometric? Check all that apply

Which sequences are geometric? Check all that apply.

a. 10, 7.5, 5.625, 4.21875, …
b. 160, 40, 10, 2.5, …
c. 20, 70, 245, 857.5, …
d. 13, 16.5, 20, 23.5, …
e. 5, 5.5, 6.05, 6.655, …
f. 16, 17.1, 18.2, 19.3, …