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

A. U

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

A. I

Identify the missing letter in the series: Z, X, V, T, ?

B. S

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

B. H

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

B. H