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

A. U

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

A. R

What letter should replace the question mark in the series: m, n, p, q, ?

A. R

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

B. H

Complete the series: B, D, F, H, ?

C. I