From the alternatives, it is clear that the series can be divided in to 4 groups of four terms each - each group comprising of three letters and a number at the third place.
D _ 6E/GP _ H/J _ 12K/MB15 _
Studying the pairs 6E and 12K, we find in each group the number is one more than the number represents the position of the letter at the forth place, in the English alphabet.
Thus, putting A = 1, B = 2, ......y = 25, Z = 26,
We have,
2nd missing tertm = H + 1 = 8 + 1 = 9;
4th missing term = 15 - 1= 14th letter = N
Thus , the 2nd and 4th missing terms are 9 and N respectively, which are given only in (4).

From the alternatives, it is clear that the series can be divided in to 4 terms each - each group comprising of two numbers followed by two letters, as shown below
23 B _ / 6 _ F G/_ 5 D _ / 8 _ H I
Clearly, the first number in each group represents the position of the letter at the third place, in the English alphabet. Thus, the third missing term is the number corresponding to the position of D in English alphabet i.e., 4, which is given in (1).
Substituting other terms of (1) into the series, wer get:
23BC/67FG/45DE/ 89HI
Observe that the second number in each group represents the position of the letter at the fourth place, in the English alphabet.

The series is abcdd/abccd/abbcd/a.

The series is abccab/bcaabc/abccab.
Thus, the pattern 'abccab/bcaabc' is repeated.

From the alternatives, it is clear that the series can be divided in to 4 groups of four terms each - each group comprising of two letters and two numbers, occurring alternately..
F _ U6/ _ 9I _ / T7 _ 20 / _ 4D23
4D indicates that in a group, the number at the second place denotes the position of the letter at the third place, in the English alphabet.
T7 _ 20 indicates that in a group, the number at the fourth place denotes the position of the letter at the first place, in the English alphabet.
Thus, putting A = 1, B = 2......Y = 25, Z = 26. we have ,
1st missing term = U = 21;
3rd missing term = 7th letter = G
5th missing term = 23 letter = W.

From the alternatives, it is clear that the series can be divided in to 5 groups of three terms each - each group comprising of two letters followed by a number.
Z _ _ 25/ YB23 / XC _ _ / W _ 19 / _ E 17
Observing the group Y B 23, we find that in a group, the number is the difference of the numbers representing the positions of the two letters in the English alphabet.
Thus, putting A = 1, B = 2, ......Y = 25, Z = 26, we have
Y - B = 25 - 2 = 23.
Similarly, missing term in 1st group = Z - 25 = 26 - 25 = 1 = A So, the first and second missing terms are A and 21 respectively, which are given only in (A).

The series is aabcc/ccabb/bbcaa.

The series is aab/aaab/aaaab/aaaaab.
Thus, the number of a's increasing by one in the successive sequence,

acbd/bacd/bcad/dcda/bacd
So, option (A) is correct.

From the alternatives, it is clear that the series can be divided in to 5 groups of four terms each - each group comprising of three letters and a number.
XWC _ /TS20 _/P12 _ L/15K _ P/_ GS7
Observing the above series, we find that each group consists of two consecutive letters and the number represents the position of one of these letters in the English alphabet.
So, 1 st missing term must be the number corresponding to W or X i.e., 23 or 24.

The series is man/man/man/man/man. Thus, the pattern 'man' is repeated.

The series is bbccaa/ccaabb/aabbcc. Thus, the letter pairs move in a cyclic order.

The series is abcd/bcad/cabd/abcd/bcad/cabd. Clearly, each group consists of letters of the previous group in the order - second, third, first and fourth.

The series is aabcc/bbcaa/ccabb/aabcc. Thus, the letters move in a cyclic order and in each group, the middle letter occurs only once.

The series is abc/b/bca/c/cab/a/abc/b.

The series is mno/nopq/opqrs/pqrst.

The series is aabab/cabcd/dcbac/babaa. Thus, the letters equidistant from the beginning and the end of series are the same.

The series is acdb/dacb/cdab/acdb/da. Clearly, each group of four letters contains the letters of the previous group in the order - third, first, second and fourth.

The series is tst/tst/tst/tst. Thus, the pattern 'tst' is repeated.

The series is nnmm/nnmm/nnmm/nnmm. Thus, the pattern 'nnmm' is repeated.