I would choose C.
A isn't the best of option because it does not directly mention fresh vs. salt water.
B does not make sense because it is discussing introduced species not native ones.
And D literally just has no relevance.
I would go with C because it is literally drawing attention to introduced species because of dumping ballast waters.
Stomata
All plant leaves need to breathe. The exchange of atmospheric gases is essential to photosynthesis, the process by which plants use sunlight to convert carbon dioxide and water into oxygen and fuel. Openings called stomata make this possible.
Hope this helps