An important takeaway from the fMRI discussion is how brain activity is measured. It is not that some areas of the brain light up and others shut down entirely during certain activities. Rather, they start with a control state of the brain, and calculate how this changes during an activity. A region that is not being used would simply not increase its oxygen use significantly. However, the passage never suggests that such a region would use "close to zero" oxygen. This is a strong statement that we would need some direct support for.
Also, consider line 48: "... this method obscures the fact that the entire brain is active in both conditions." This directly contradicts answer choice B. The regions of the brain that are not used for a particular task are still active.
