In a certain code language, '851' means 'good sweet fruit' ; '783' means 'good red rose' and '341' means 'rose and fruit'. Which of the following digits stands for 'sweet' in that language ?

Justification:      

In the first and second statements, the common code digit is '8' and the commmon word is 'good'.

So, '8' means 'good'.
In the first and third statements, the common code digit is '1' and the common word is 'fruit'.
So, '1' means 'fruit'.
Thus, in the first statement, '5' means 'sweet'.