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

The given series consists of 12 positions: L _ _ L _ M _ L _ _ M _
Let's test the options to find a repeating or logical pattern:

Testing Option B (MMLMLML):
Placing the letters sequentially gives:
L M M L L M M L L M M L

Let's break this series into groups of 3 letters:
LMM | LLM | MLL | MML → No clear simple repetition.

Let's break this into groups of 4 letters:
LMML | LMML | LMML

Here we can see a clear repeating pattern of 4 letters: LMML.

Let's verify the blanks filled by Option B:
1st blank: M
2nd blank: M
3rd blank: L
4th blank: M
5th blank: L
6th blank: M
7th blank: L

The letters filled are M, M, L, M, L, M, L which matches Option B.