These questions are based on letter series in which some of the letters are missing. The missing letters are given in the proper sequence in one of the alternatives among the four given under each question. Find out the correct alternatives for each questions.

__ ab __ a __ bb __ ab __ a __

Three of the following four letter-clusters are alike in a certain way and one is different.

Select the odd one.

Which letter will replace the question mark (?) in the following series?

B, D, G, I, L, ?, Q

Which letter cluster will replace the question mark (?) in the following series?
CGE, HJI, LPN, SUT, ?

Select the option that will fill in the blank and complete the given series.

DXB, GSI, JNP, MIW, _____

If the following words are arranged as per their order in the English dictionary, which word will fifth in the sequence?

1. Weekly
2. Weather
3. Weird
4. Weaver
5. Weight
6. Wielded

Select the letter-cluster that can replace the question mark (?) in the following series.

FIY, HLD, JOI, LRN, NUS, $?$

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

1. IV
2. VI
3. VII
4. VJ 

 In the word "DOUBLE" two letters are such that number of letters between those two letters is as many as numbers of letters of alphabet. Find those two letters.

(A) B, E

(B) E, U

(C) O, L

(D) D, B