The correct option is
A I was helped by a very old friend.
In order to convert the given question into passive voice, let's understand the difference between active and passive voice.
Active voice emphasises on the person who does the action, whereas passive voice emphasises on the action itself. For example:
Active: The thief stole my car.
Passive: My car was stolen by the thief.
The object 'My car' comes first and the subject 'the thief' is put after the verb in the passive voice.
The doer in the given sentence is: 'A very old friend' (We use 'a very old' with 'friend' because it describes the word - 'friends'.)
The verb in the given sentence is: 'helped'
The receiver of the action in the given sentence is: 'me'
In the passive voice, the receiver becomes the subject. Right after the subject, we place a verb and then the receiver of the action (object) and the remaining clause, if any. We also use 'by' before the object to show that the action was performed by the object.
As the given sentence in the active voice is in the simple past tense, we will use 'was/were' and the verb in the past participle form to form the sentence in the simple past tense in the passive voice.
We can't use 'Me' as the subject of the sentence as it is always used as the receiver of the action. Hence, we will use 'I' here which is a subjective pronoun, instead of the objective pronoun 'me'.
Hence, 'I was helped by a very old friend.'
Thus option B, C and D are incorrect.
CORRECT ANSWER - A - 'I was helped by a very old friend.'