Consider the following arrangement that has some missing letters:

abab_b_bcb_dcdcded_d

The missing letters which complete the arrangement are

By examining the sequence and trying various options, we can discern that the correct sequence follows a repeated pattern of ababa, bcbcb, cdcdc, deded. Only option (c) matches this pattern.

If we were to choose option (a), the sequence would be ababa, bbbcb, cdcdc, deddd—there is no discernible pattern in it.

Option (b) would yield the sequence ababa, bbbcb, ddcdc, deded—again, there is no recognizable pattern.

Similarly, option (d) results in ababb, bcbcb, ddcdc, deded—lacking a clear repeating pattern.

Therefore, the correct choice is (c) as it aligns with the observed repeated pattern.