Possible explanation:

Given sequence:
c_accaa_aa_bc_b

Observations:
- The sequence contains 14 characters, including underscores as placeholders for missing characters.
- The letters are grouped in various combinations, separated by underscores.
- The first and last characters are fixed as 'c' and 'b', respectively.
- The second character is a placeholder, which can be any letter except 'c' or 'b', because the second and last-but-one groups have distinct letters.
- The third and fourth characters are both 'a', indicating a repeated pattern.
- The fifth character is another placeholder, which can be any letter except 'a' or 'b', because the fifth and last-but-two groups have distinct letters.
- The sixth to eighth characters form a repeated pattern of 'a', 'a', and a placeholder, which can be any letter except 'a' or 'b', because the eighth and last-but-three groups have distinct letters.
- The ninth and tenth characters are both 'b', indicating a repeated pattern.
- The eleventh character is another placeholder, which can be any letter except 'a' or 'b', because the fifth and last-but-two groups have distinct letters.
- The twelfth to fourteenth characters form a repeated pattern of 'c', 'b', and a placeholder, which can be any letter except 'c' or 'b', because the twelfth and first groups have distinct letters.

Options and analysis:
a) abba - This option does not fit the pattern, because it has two 'b's in the second group and two 'a's in the fifth group, which violate the distinctness condition.
b) cbbb - This option fits the pattern, because it has a 'c' in the first group, four 'b's in the second group, two 'a's and a 'c' in the third to fifth groups, two 'b's in the sixth group, a 'c' and a 'b' in the seventh and eighth groups, a 'b' and a 'a' in the ninth and tenth groups, a 'c' and a 'b' in the eleventh and twelfth groups, and a 'b' in the last group.
c) bbbb - This option does not fit the pattern, because it has four 'b's in the first group, which is not allowed.
d) cccc - This option does not fit the pattern, because it has four 'c's in the first group, which is not allowed.

Therefore, the correct answer is option 'B'.