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

C. Q

Complete the series: B, D, F, H, ?

A. J

What comes next in the series: M, O, Q, S, ?

B. T

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

A. U

Find the missing number in the series: 5, 10, 20, 40, ?

D. 80