What letter comes next in the series: a, e, i, o, ?

A. U

Find the odd one out in the series: A, D, G, J, M, P, S

D. S

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

A. R

What letter should come next in the series: B, D, F, H, ?

A. J

A, E, I, O, ?

A. U