1. 1,3,9,27,81
1*3=3
3*3=9
9*3=27........⇒ Geometric, common ratio is 3 --- B
3. 20,17,14,11
20 - 3 = 17
17 - 3= 14
14 -3= 11........⇒ Arithmetic , common difference is 3 ....D
4. 128, 32, 8, 2
32=128*1/4=128*0,25
8=32*0,25
2=8*0,25.......⇒ Geometric, common ratio is 0,25.......A
