Start with the rule itself: a person who makes a claim before a court carries the burden of proving that claim, the other side does not have to disprove it first. The next step is to identify exactly who is asserting what in these facts.
A is the one approaching the court, and A's claim is specific: that B, C and D committed a particular crime. Since A is the asserting party, the burden the principle creates lands on A, and it lands on the full content of what A said, not some smaller piece of it such as mere presence at the scene.
Checking this against the four options confirms it. Requiring proof of presence only understates A's actual claim, shifting the burden onto B, C and D reverses the direction the principle points, and putting the burden on the police ignores that the police are not the party who came forward with the accusation. Only the option that has A proving the commission of the crime itself matches what the principle demands.
So the correct answer is A must prove that B, C and D have committed the crime.
A quick way to stress test an answer under this kind of principle is to ask, for each option, what extra fact would have to be true for that option to be the right outcome, and then check whether the given facts actually supply that extra fact.
Only one option requires no additional or altered fact to hold true, and that is the one tying the burden directly to A and to the full content of A's own claim.
Therefore, the correct answer is A must prove that B, C and D have committed the crime.