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

A. U

What letter should replace the question mark in the series: b, d, f, h, ?

A. J

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

A. U

Find the missing number in the series: 5, 10, 20, 40, ?, 160.

C. 80

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

A. J