What letter comes next in the series: z, x, v, t, ?

A. S

Complete the series: m, n, o, p, ?

A. Q

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

A. U

Find the missing letter in the series: m, n, p, q, ?

A. R

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

A. J