How did Scoville and Milner conclude the hippocampus was the key structure in the amnesic syndrome?

1. they had patients with only the hippocampus damaged and they showed the deficit
2. they showed that only parts of the brain connected to the hippocampus really mattered
3. they measured the amount of hippocampus left and showed it predicted how much memory was spared
4. they didn't make this conclusion
5. they showed that the amount of hippocampus damage seemed to predict the amount of deficit.