Which numerical pattern is a linear progression? 1 2 , 2 3 , 3 4 , 4 5 , . . . 1 2 , 2 3 , 3 4 , 4 5 , . . . 1, 3, 7, 13, . . . 1, 3, 7, 13, . . . − 10 , − 20 , − 40 , − 80 , . . . − 10 , − 20 , − 40 , − 80 , . . . 18, 26, 34, 42, . . . 18, 26, 34, 42, . . .