The correct option is A 8731
In the first statement, the code digit '1' as well as the word 'the' occurs twice. So, '1' is the code for 'the'.
In the first and fourth statements, the common code digits are '1' and '3' and the common words are 'the' and 'dog'. Since, '1' stands for 'the', so '3' is the code for 'dog'.
Thus in the fourth statement, '4' is the code for 'ran'.
In the second and third statements, the common code digits are '1' and '6' and the common words are 'the' and 'cat'. Since '1' stands for 'the' , so '6' is the code for 'cat'.
In the first and third statements, the common code digits are '1', '6' and '2' and the common words are 'the', 'brown' and 'cat'. Since '1' and '6' stands for 'the' and 'cat' respectively, so '2' is the code for 'brown'.
Thus, in third statement, '7' is the code for 'was'.
In the first and second statements, the common code digits are '1', '6' and '8' and the common words are 'the', 'cat' and 'frightened'. Since '1' and '6' stands for 'the' and 'cat' respectively, so '8' is the code for 'frightened'.
So, code for 'the dog was frightened' is 8731.
Hence, option (B) is the correct answer.