What letter comes next in the series: z, x, v, t, ?

A. S

Find the missing number in the series: 5, 10, 20, 40, ?

C. 80

What letter comes next in the series: b, d, f, h, ?

C. I

What number should replace the question mark in the series: 2, 4, 8, 16, ?

C. 32

Identify the missing term in the series: 1, 1, 2, 3, 5, ?

B. 8