Answer choice C

Hi @amarachicynthia, Happy to help! What C is saying is that the chemical killed not only the native species of oyster, but also a separate imported species. Now that the waters are warmer, this imported species is flourishing "at the expense of" the native species in question. or in other words, taking over the ecosystem and making it harder for the native species to survive. Hope this helps. Let me know if you have anymore questions! Andrea