Which letter is out of place in the series: A, B, D, C, E?

D. D

What is the next letter in the series: A, E, I, M, ?

A. O

What is the missing term in the series: 100, 90, 80, 70, ?

A. 60

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

B. H

E, G, I, K, ?

A. M