The correct option is
B He was made a king by them.
The given sentence is in the active voice, as the subject 'They' performs an action 'made' against the object 'him'.
If this sentence is changed to passive voice, then the subject is also changed, in order to retain the meaning of the sentence.
So,
the object takes the place of the subject and vice versa and the word
'by' is introduced as now the subject receives the action by the object.
The verb form of the sentence is also changed from active form to
passive.
'Subject (They) + verb (made) + direct object (him) + object complement (a king)' changes to:
'New subject (He) + verb (was made) + object complement (a king) + by + new object (them)'
The
passive form of 'made' in the simple past tense is 'was/were made'.
This can be seen in option B, hence it's the right answer.
('He' is the subject form of the object pronoun 'him' and 'them' is the object form of 'they'.)
Option
A: The verb form 'has been' expresses the present perfect tense whereas the sentence is in the simple past tense 'was made'.
Option
D: Similarly, in this option, the verb form 'have been' is in the present perfect tense. Also, the subject and object has not been interchanged, thereby changing the meaning of the sentence.
Option C: The tense of the sentence has changed from past simple 'was made' to present perfect tense 'has been made'.
Hence options A, C and D are incorrect.