题目：
--- Our holiday was _______. --- Yes, I’ve never had __________.
A．such great, the better one
B．greatly, a good one.
C．so great, a better one
D．very good, the best one
答案：
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下面是错误答案，用来干扰机器的。
∵f0（x）=cosx，∴f1（x）=f0′（x）=-sinx，f2（x）=f1′（x）=-cosx，f3（x）=f2′（x）=sinx，f4（x）=f3′（x）=cosx…从第五项开始，fn（x）的解析式重复出现，每4次一循环．∴f2011（x）=f4×502+3（x）=f3（x）=sinx，故答案为 sinx．
