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

C. I

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

C. I

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

A. S

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

C. 80

What letter comes next in the series: b, d, f, h, ?

C. I