The strings with the 1st, 4th and 7th bits as 1’s will be
1001D001
1001D011
1001D101
1001D111
1011A001
1011A011
1011A101
1011A111
1101A001
1101A011
1101A101
1101A111
1111A001
1111A010
1111A101
1111A111
The first four are accepted. In the remaining three block of fours only the first string is accepted.
The total number of strings accepted are 7 which is option (C)