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

A. R

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

A. U

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

B. H

What letter should replace the question mark in the series: z, x, v, t, ?

A. R

Complete the series: a, e, i, o, ?

A. U