The main argument in this passage is that the Antarctic must be left unexploited.

Option (b) can be eliminated. Several scientific studies can take place there, regardless of how unique or common the environment there is.

Option (c) can be eliminated as they do not need to study the place only to find correlations to the rest of the planet.

Option (d) merely adds more data.

Option (a) seems to be the most logical answer as the main objective of the treaty is to protect Antarctic region from environmental exploitation. If the scientific activities there are causing harm, then they need to be discontinued.

Hence, the correct answer is option a.