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

A. U

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

B. H

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

A. J

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

B. H

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

A. J