The argument is basically saying that lots of people don't care much about the conservation of threatened species. The argument brings up the bald eagle and says that if we focus conservation efforts around it (since it inspires people and fosters in them a sympathetic attitude toward the needs of other threatened species), this will eventually bring attention to the conservation of all kinds of threatened species.
In a sense, yes, this argument is arguing by saying if there's a certain cause, there'll be a certain effect.
It's tough to identify the conclusion on this question, but we just need to make sure we stay focused on thinking which statement supports which. The goal of the argument is to garner more support for conservation efforts. Without sympathy, that support isn't going to be obtained (this is the second claim of the argument). However, the bald eagle is capable of garnering that sympathy (this is the first claim of the argument). Thus, the bald eagle is the best threatened species to start conservation efforts with (this is the third claim and is the conclusion of the argument). This leads us to (B), which states, "The conservation of bald eagles is the first necessary step in conserving other endangered species." (B) does a great job of summarizing the third sentence of the stimulus, which is the main point, so it's the correct answer choice.
Does this make sense? Let us know if you have any other questions!