The two ways of relating what a person has said are 1)direct and 2)indirect (reported).
In the direct speech, the exact words of the original speaker are repeated.
In the indirect speech (reported speech), the exact meaning of what the speaker told is expressed but not necessarily in the speaker’s exact words.
Option C is correct as the appropriate introductory verb 'asked' is used with the conjunction 'if' and the helping verb 'were'.
Options A, B, and D are wrong as 'that' cannot be used,'told' cannot be used', and 'these' is not transformed to 'those' respectively.
The correct answer is C)Rahul asked if those mangoes were sweet..