Select the combination of letters that when sequentially placed in the blanks of the given series will complete the series.
cc_d_ch_c_h _ch

Let's count the total number of characters including blanks: 16 slots.
Let's divide the series into groups of 4:
_ c c _ | d _ c h | _ c _ h | _ _ c h

Let's look at the patterns:

The second group is d _ c h.

The fourth group ends with _ _ c h.
This suggests a repeating pattern of 4 letters, likely d c c h.

Let's test the pattern d c c h for all 4 groups:

d c c h (Blanks filled: 1st → d, 4th → h)

d c c h (Blank filled: 6th → c)

d c c h (Blanks filled: 9th → d, 11th → c)

d c c h (Blanks filled: 13th → d, 14th → c)

The sequence of letters filled in the blanks is: d, h, c, d, c, d, c → dhcdcdc.
This matches Option D perfectly.