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

A. U

What letter should come next in the series: a, c, e, g, ?

B. H

What letter should replace the question mark in the series: a, e, i, o, ?

A. U

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

A. J

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

C. Q