The answer is A. The sulfur-filled fluid that comes from the vents is lethal to some animals.
Deep-sea vents are hydrothermal vents at the bottom of the oceans. The mineral water that comes from them is rich in sulfide and methane and can be lethal to the most of animals. However, some bacteria are able to survive in such conditions thanks to the process of chemosynthesis. Chemosynthesis is a process in which some bacteria produce sugar, similarly to photosynthetic process. But, while in photosynthesis the energy of Sunlight is used to convert carbon dioxide and water into sugar and oxygen, in chemosynthesis, carbon dioxide, oxygen, and hydrogen sulfide are used to produce sugar, along to water and sulfur. This process is preferable when there is no light and the environment is rich in sulfide or methane, such in deep sea vents.
