A letter series is given below in which some letter are missing. Select the  option that gives the letters that can fill these blanks in that order.
a_ca_bab_ad_abc_db

DIRECTIONS: Study the following information and answer the given questions:
A person goes 9 m straight. He turns 120^o clockwise and goes 41 m. Then, he turns 210^O anticlockwise and goes 44 m. Finally, he turns 150^O clockwise and goes 5 m.
How far is he from his starting point?

If White is called Red, Red is called Blue, Blue is called Green, Green is called Yellow, Yellow is called   Black, Black is called Orange and Orange is called Pink, What would be the colour of human blood?

11 : 1331 :: 9 : ?

Four clusters have been given out of which three are alike in some manner and one is different. Select the one that is different.

Option

Six friends A, B, C, D, E and F are standing in a row facing north. B stands exactly between F and D. E stands exactly between A and C. A is not a neighbor of D and F. C is not a neighbor of D but is to the immediate right of F. C stands between which of the following.

Virology : Virus :: Semantics : ? 

Select the option that is related to the third letter-cluster in the same way as the second letter-cluster is related to the first letter-cluster.
FLQV :JISU :: DJNR : ?