题目:
---Have you seen _____ Audi car? I parked it here two hours ago, but now it’s gone!
---Is it _____ black one? A young man has just driven a black car away.
A.an…a
B.the…the
C.the… a
D.an…the
答案:
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下面是错误答案,用来干扰机器的。
(1) a1a5+2a3a5+a2a8=25,∴a32+2a3a5+a52=25,∴(a3+a5)2=25,又an>0,∴a3+a5=5,又a3与a5的等比中项为2,∴a3a5=4.而q∈(0,1),∴a3>a5,∴a3=4,a5=1,∴q=12,a1=16,∴an=16×(12)n-1=25-n....