Explanation:

Here’s what’s really happening with the sequence:

cd_ab_cd_abb_dda_b

Let’s try to fill the blanks one by one, using each option by slotting the letters in, left to right.

Option 1: dbdcb

Slots in like this: cddabbcddabbcddabb

? Which gives:

cddab b cddabbc ddabb

That jumbles words—it doesn’t fit the pattern.

Option 2: bbcdb

Sequence: cdbabbcdcabbdddabb

? cd bab bcdc abbd ddabb

Still messy; doesn’t fit clean letter groupings.

Option 3: dbcbc

Plug them in: cddabbcdcabbbddacb

? cd dab bcdc abbb ddacb

Pattern is still off.

Option 4: cbdab

Let’s see: cdcabbcddabbaddabb

? cdcabb cd d abba ddabb

Now this is more promising! "cdcabb cd d abba ddabb" mirrors the c-d/a-b repeating chunks.

The thing to catch: the sequence repeats “cd”, “ab”, + one/two letters over and over. Only Option 4 truly fits the rhythm and forms reasonable words/fragments.

Quick summary of the options:

- Option 1 (dbdcb): Makes it messier. No clear repeat.

- Option 2 (bbcdb): Random scattering, can’t spot the structure.

- Option 3 (dbcbc): Similar randomness.

- Option 4 (cbdab): Chunks fit, mirrors the repeating pattern.

Correct Answer:

Option 4: cbdab