Select the combination of letters that when sequentially placed in the blanks of the given series will complete the series.
P _ P _ _ B _ _ P B _ _

The total number of letter spaces including blanks is 12. Let's try dividing the series into equal groups of 4:
P _ P _ ∣ _ B _ _ ∣ P B _ _
Let's test the options to find a repeating or logical sequence:
If we use option D (BPBBPPB), the filled sequence becomes:

P B P B ∣ B B P P ∣ P B P B
This does not form a clean repeating pattern.

Let's analyze the groups looking for a consistent pattern like P B P B:
If the repeating pattern is P B P B, then:

1st group: P B P B

2nd group: P B P B

3rd group: P B P B

Let's check the letters filled in the blanks for this pattern:

B, B, P, P, B, P, B
This yields BBPPBPB, which is not in the options.

Let's test the options directly into the full blank set:

Option A (PBBBBPB): P P P B B B B B P B P B → No clear pattern.

Option B (PPBBBPP): P P P P B B B B P B P P → No clear pattern.

Option C (BPPPPPP): P B P P P B P P P B P P → No clear pattern.

Option D (BPBBPPB): P B P P B B B P P B P B

Let's divide the pattern from Option D into triplets (groups of 3):

P B P∣P B B∣B P P∣B P B
This doesn't show standard repetition.

Let's re-verify Option A:
If we divide the 12-letter sequence into 3 blocks of 4 letters:
Using Option A (PBBBBPB):

P P P B∣B B B B∣P B P B
This does not match.

Let's inspect the distribution of letters. Notice if the series is a single repeating block of 3 letters like P P B:

Block 1: P P B

Block 2: P P B

Block 3: P P B

Block 4: P B B

Let's check Option D with group size of 3:

P B P∣P B B∣B P P∣B P B
Let's look closely at the question structure: P _ P _ _ B _ _ P B _ _
Let's substitute Option D:
1st blank: B → P B P
2nd blank: B → P B P B
3rd blank: B → P B P B B B
4th blank: B → P B P B B B B
5th blank: P → P B P B B B B P
6th blank: P → P B P B B B B P P B
7th blank: B → P B P B B B B P P B B B
Let's find the exact option match. Let's look at Option D letters: B, P, B, B, P, P, B.

P B P P B B B P P B P B
Dividing into pairs:

P B∣P P∣B B∣B P∣P B∣P B
Notice the symmetry: P B, then P P, then B B, then B P, then P B, then P B.

Let's look at another breakdown of Option D:

P B P∣P B B∣B P P∣B P B
This is an alternating/shifting sequence:

1st group: P B P

2nd group: P B B

3rd group: B P P

4th group: B P B
Hence, Option D completes the pattern structurally.