Although you should not misinterpret this, Barbour and Wright actually say that Option B is the right answer. We would not typically think that this is right because Americans are supposed to act as individuals. We prize individuality, not group consciousness or group-oriented behavior. Even so, these authors say that Americans act as ideal citizens when they act as a group. The authors mean that Americans are more likely to act ideally as a whole group than they are to act ideally as individuals.
Barbour and Wright argue that there are two views of American citizenship. One says that Americans are self-interested actors who try to pursue their own goals. The other says that they are able to act together to pursue the common good. The authors say that these two visions can come together. People bring their own goals, but they discuss their goals and opinions and come to a group decision about what to do. This is why, on p. 400, they say that “Americans as a group often behave as ideal citizens, even though as individuals they do not.”