In a certain code language, '3a, 2b, 7c' means 'Truth is Eternal';

'7c, 9a, 8b, 3a' means 'Enmity is not Eternal'  and

'9a, 4d, 2b, 8b' means 'Truth does not perish'.

Which of the following means 'enmity' in that language ?

The first three letters are coded as same positioned letters from the right end of the alphabet. So are the seventh to tenth letters. The fourth , fifth and sixth letters move one, two and three positions forward respectively in the alphabet. So, do the last three letters. Thus,

CONCENTRATION => XLMDGQGIZGJQQ

Now reverse this and we get QQJGZIGQGDMLX

In the first and second sentences common word is Dogs and common code is Kun. In the first and third sentences common word is are and common code is Tom. Therefore Sud = baking

nec po tam => boys are studying

me tam sam => grapes are sour

tam po me => boys are grapes 

It is clear that "sam" represents "sour" in that code language.

Movement of letters  is +1, +2, +3, +4, +5

Therefore, SMILE => TOLPJ

- There are 8 letters in the word.

- The coded word can be obtained by taking the immediately following letters of word, expect the first and the last letters of the given word but in the reverse order. That means, in the coded form the first and the last letters have been interchanged while the remaining letters are coded by taking their immediate next letters in the reverse order.

- There are 7 letters in the word

- The middle letter has been left intact

- The first and the last letters  of the word have interchanged their position. Similarly, the second and the third letters and the fifth and sixth letters have interchanged their position.

Justification: 

In the first and second statements, the common code digit is '4' and the common word is 'good'.

So, '4' stands for 'good'.
In the second and third statements, the  common code digit is '7' and the common word is 'pictures'.
So, '7' means 'pictures'.
Thus, in the second statements, '8' means 'see'.

Justification:      

We can find the code for 'home' from the second and third statements.

For finding the code for 'they', we need the code for 'go' which cannot be determined from the given data.
Clearly, statement A is not necessary.