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

A. S

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

A. Q

What letter should replace the question mark? x, u, r, o, ?

C. N

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

B. H

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

A. R