Why not B

@GLEE, Great question. Before looking at why C is correct and why B is wrong, let's take a look at the stimulus to make sure we have a firm grasp on the argument and conclusion. The economist begins by presenting his colleagues' argument: in order to stimulate economic growth, interest rates should be further lowered. She then introduces her argument, stating that no such stimulation is needed. Why? She supports this conclusion with the premise that the economy is already growing at a sustainable rate. She then adds that currently there is no other reason to lower interest rates further, which is her main conclusion. (The other conclusion in her argument is the subsidiary conclusion, which supports her main conclusion). That doesn't sound like a reasonable conclusion. She's told us that lowering interest rates isn't needed to stimulate economic growth. In telling us this, she has eliminated a single possible reason for reducing interest rates. However, she then makes the conclusion that there is no other reason to lower interest rates, which is far too sweeping of a conclusion when she only eliminated one possible reason for reducing interest rates. In order for this argument to make sense, she must be assuming that there is no other reason for reducing interest rates further. But what if there are other reasons for reducing interest rates further? This is the flaw with her argument. Now that we have a firm grasp of the argument, let's look at the answer choices. Answer B is incorrect because the economist does not confuse economic growth with what stimulates it. The economist's colleagues are arguing for a further reduction in interest rates to stimulate the economy more, but the economist is saying that no stimulation is needed because the economy is growing at a sustainable rate. The economist is not confusing economic growth with what stimulates it in stating this. We can get rid of this answer. Answer C says that the economist presumes that a need to stimulate economic growth is the only possible reason to lower the interest rates further. This is exactly what we identified as the flaw in the economist's argument. The economist eliminates one possible reason for reducing interest rates and concludes from the elimination of this single reason that there is no reason at all for lowering interest rates further. This is too far of a reach, which is why the argument is flawed. C is our answer. Does this make sense? Let us know if you have more questions!