Explanation:

Let’s break it down step by step:

- We need to find which option, when its letters are slotted into the blanks of:

_ c _ b d _ c b c d a _ a _ d b _ a

completes a correct, consistent series.

- Here’s the letter pattern with 6 blanks, so the right option should have 6 letters.

Now, let’s test each:

Option 1: acbcad

Put these in: a c a b d c b c d a c a d b c a

This looks wonky—doesn’t fit a pattern.

Option 2: cdebad

Put these in: c c d b d e c b c d a b a d b a

Too random. Still not right.

Option 3: bdbcba

Try this: b c b b d b c b c d a b a b d b a

Still doesn’t look consistent or form a sequence.

Option 4: adabed

Let’s try it: a c d b d a c b c d a a d b e d a

Now check the pattern: you can see the sequence c-b-c-d, and the inserted letters repeat in a logical way.

So, the correct answer is:

Option 4: adabed