Answer : 4. "The case is being argued very effectively by our advocate."
Explanation :

In Active Voice, a sentence emphasizes the subject, performing an action.
In Passive Voice, a sentence emphasizes the action or the object of the sentence.
The given sentence is in the active voice and 'our advocate' is the subject and 'the case' is the object.
When we convert this sentence into passive voice, the subject 'our advocate' of the active voice becomes the object, the object 'the case' becomes the subject.
The passive format "is + being + V3 (argued)" should be used.
This is the active and passive voice rule for the present continuous tense.