• The sequence provided is A_BCD_BBCDABC_DABC_D.

Step 1: Counting Elements: 

• The sequence has 20 elements, including spaces, which are counted as separate elements.
• There are high chances that it will be sequenced as a group of 4 or a group of 5.

Step 2: Checking in a group of 4 elements, including spaces

• A_BC
• D_BB
• CDAB
• C_DA
• BC_D
• There are five such groups. We do not observe any sequence. 

Step 3: Checking in a group of 5 elements, including spaces

• A_BCD
• _BBCD
• ABC_D
• ABC_D
• Here, we find D in the last of every group. It means that we are on a good path.

Identifying Patterns: The pattern noticed is that in each group of five elements, the second element is doubled:

• First group: A, A, B, C, D (Double A)
• Second group: A, B, B, C, D (Double B)
• Second group: A, B, B, C, D (Double B)
• Third group: A, B, C, C, D (Double C)
• Fourth group: A, B, C, D, D (Double D)

According to the pattern observed, option (c) A, A, C, D is the correct answer.