Given Information:
- The code word for 'DOG' is 'BCMNEF'.

Approach:
To find the code for 'CAT', we need to identify the pattern or rule used to encode the word 'DOG' into 'BCMNEF'.

Analysis:
Let's analyze the given code word 'BCMNEF' and the word 'DOG' to identify the pattern.

1. Position of letters:
- The first letter of the code word 'B' corresponds to the letter 'D' in 'DOG'.
- The second letter 'C' corresponds to 'O'.
- The third letter 'M' corresponds to 'G'.

2. Shift in alphabets:
- The letter 'B' is one step ahead of 'D' in the alphabet.
- The letter 'C' is one step ahead of 'O'.
- The letter 'M' is one step ahead of 'G'.

3. Reverse order:
- The letters in the code word 'BCMNEF' are in reverse order compared to the letters in 'DOG'.

Pattern:
Based on the analysis, we can identify the following pattern to encode the word:
- Take each letter of the word.
- Shift the letter one step ahead in the alphabet.
- Write the letters in reverse order.

Applying the Pattern:
Now, let's apply the identified pattern to the word 'CAT' to find its code.

1. Position of letters:
- The first letter 'C' corresponds to the first letter of the code word.
- The second letter 'A' corresponds to the second letter.
- The third letter 'T' corresponds to the third letter.

2. Shift in alphabets:
- The letter 'C' is one step ahead of 'B' in the alphabet.
- The letter 'A' is one step ahead of 'Z'.
- The letter 'T' is one step ahead of 'S'.

3. Reverse order:
The letters in the code word 'ABYZRS' are in reverse order compared to the letters in the word 'CAT'.

Code for 'CAT':
Therefore, the code for 'CAT' is 'ABYZRS', which is option 'D'.