Which sequences are geometric sequences?

Check all that apply.

4, 2, 1, 1/2,1/4, ...

-2, 3, - 4, 5, - 6, ...

2, 6, 18, 54, 162, ...

-4, - 16, - 64, - 256, ...

-2, - 4, - 12, - 48, - 240, ...

1.) 4, 2, 1, 1/2,1/4, ... 2.) 2, 6, 18, 54, 162, ... 3.) - 4, - 16, - 64, - 256, ... are geometric sequences because common ratio is same. Example: 1.) ratio of 1st and 2nd term is 1/2. similarly ratio of 3rd and 4th term is 1/2 and so on.

a, c, d - correct answers for sure