Complete the series: a, c, e, g, ?

B. H

Find the missing letter in the series: z, x, v, t, ?

A. R

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

C. 80

What number should replace the question mark in the series: 1, 1, 2, 3, 5, ?

A. 7

Identify the missing number in the series: 3, 6, 11, 18, ?

A. 25