General Lee had ordered his Confederate army to invade the northern state of Pennsylvania in the hope of enticing the Union army into a vulnerable position. The strategy was also aimed at increasing the war weariness of the North and ultimately at leading Abraham Lincoln's government into concluding a peace deal and recognizing the independence of the Confederate South.
In my mind there is a subtle difference in "wait and see" and a defensive strategy. In most instances, "wait and see" would imply no action but watch and react. On the other hand "defensive strategy" would imply defend your resources when you cannot destroy your enemy's resources/artillery whatever. The last sentence in first paragraph implies that offensive strategy failed and therefore, states were forced to adopt a defensive war policy. I think that is why C is correct and D is not.
I hope it helps.