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

B. H

Identify the missing letters in the series: a, e, i, o, ?

A. U

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

C. 80

Find the missing number in the series: 5, 11, 23, 47, ?, 191

C. 97

Find the missing letter in the series: b, d, f, h, ?

A. J