What is the next letter in the series: A, C, E, G, ?

B. H

A, E, I, M, ?

A. O

What is the missing number in the series: 2, 4, 8, 16, ?, 64

B. 32

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

D. 80

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

B. 8