Find the missing (?) in the series.
NA, PC, RE, TG, ?, XK, ZM

In the following question, which one set of letters when sequentially placed at the gaps in the given letter series shall complete it?
gh_i_hi_ig_ii_ _

Select the term that will come next in the following series.
11, 13, 17, 23, 31, 41, 53, 67, 83 ?

18, 25, 23, 30, ?

Complete the series choosing the missing number: 

1, 9, 17, 33, ______, 73

Direction (66-70): What should come in place of the question mark(?) in the following number series?

22, 21, 23, 22, 24, 23, ?

Choose the correct alternatives from given ones that will complete the series.

8, 24, 12, 36, 18, ?