题目

阅读理解 It's not possible to stay together with loved ones all thetime. Sometimes family members have to be far away from each other. During thattime they might face something terrible. Although we know what they aresuffering, being far away makes it harder to help and comfort (安慰) loved ones. There is no use worrying a lot about them. Keeping apositive attitude of support is more helpful than getting into worrying aboutthe person. I think it is what I can do to help my loved ones. My daughter has been working full-time during summer about10 hours a day. She has to study hard for a bi函数f1（x）=cosx﹣sinx，记f2（x）=f1′（x），f3（x）=f2′（x），…fn（x）=fn﹣1′（x），（n∈N*，n≥2），则=（ ）A. B. C.0 D.2008