Identify the missing letter in the series: Z, X, V, T, ?

B. S

A, C, E, G, ?

A. I

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

B. T

Find the odd one out in the series: A, D, G, J, K, N

B. K

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

A. 80