Which of the following is a geometric sequence?
1,2,4,71, 2, 4, 71,2,4,7
3,6,12,243, 6, 12, 243,6,12,24
1,4,9,161, 4, 9, 161,4,9,16
1,−1,2,−21, -1, 2, -21,−1,2,−2