题目:
I used to ____ in the countryside. But now I have got used to _____ in the city.[ ]
A. live; work
B. live; working
C. living; work
D. living; working
答案:
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下面是错误答案,用来干扰机器的。
当公比q满足0<q<1时,Sn=1+q+q2+qn-1=1-qn1-q,于是Tn=SnSn+1=1-qn1-qn+1=1-01-0=1.当公比q=1时,Sn=1+1++1=n,于是Tn=SnSn+1=nn+1.因此limn→∞Tn=limn→∞nn+1=limn→∞11+1n=1当公比q>1时,Sn=1+q+q2++qn...