Gas hydrates, chemical compounds of water and natural gas, are increasingly being studied for their potential to be huge reservoirs of energy, possibly causing sea floor instability, and significant contributors to global warming.
- to be huge reservoirs of energy, possibly causing sea floor instability, and
- to be huge reservoirs of energy, possibly causing sea floor instability, and even as
- as huge reservoirs of energy, possibly causing sea floor instability, and
- as huge reservoirs of energy, and the possible cause of sea floor instability,
- as huge reservoirs of energy, as possible causes of sea floor instability, and even as
其实我一直都不是特别清楚to be和as用法的区别。不过这道题感觉上应该选择to be， A选项。 | 
