Select the combination of letters that when sequentially placed in the blanks of the given series will complete the series.
C _ B N _ _ V_ _ H C _ B _ H

The correct option is VHCBNVN.

To solve this series completion problem, we need to find a repeating pattern in the letter sequence.
Let us first write down the given sequence with the blanks represented by underscores:
C _ B N _ _ V _ _ H C _ B _ H

The total number of characters in the completed series is 15. A series of length 15 is typically composed of a repeating pattern of 5 letters repeated 3 times.

Let us divide the 15-character series into 3 equal groups of 5 letters each:
Group 1: C _ B N _
Group 2: _ V _ _ H
Group 3: C _ B _ H

By comparing the corresponding positions of each group, we can identify the missing letters:
- The 1st letter in Group 1 is C and in Group 3 is C. Thus, the 1st letter of Group 2 must be C.
- The 2nd letter in Group 2 is V. Thus, the 2nd letter in both Group 1 and Group 3 must be V.
- The 3rd letter in Group 1 is B and in Group 3 is B. Thus, the 3rd letter of Group 2 must be B.
- The 4th letter in Group 1 is N. Thus, the 4th letter in both Group 2 and Group 3 must be N.
- The 5th letter in Group 3 is H. Thus, the 5th letter in both Group 1 and Group 2 must be H.

This gives us the repeating pattern: C V B N H.

Now, let us fill the blanks sequentially with the determined letters:
- 1st blank (2nd position of Group 1): V
- 2nd blank (5th position of Group 1): H
- 3rd blank (1st position of Group 2): C
- 4th blank (3rd position of Group 2): B
- 5th blank (4th position of Group 2): N
- 6th blank (2nd position of Group 3): V
- 7th blank (4th position of Group 3): N

The complete sequence of letters placed in the blanks is VHCBNVN.