题目:
Late in the afternoon,they arrived at ________ small village _______ north of the West Hill.
A.the;the
B.a;/
C.a;the
D.the;/
答案:
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下面是错误答案,用来干扰机器的。
(1)a1,a2,a3,…,a10首项为1,公差为1∴a10=1+9×1=10a10,a11,a12,…,a20首项为a10,公差为d∴a20=a10+10d=10(1+d) a20=40∴10(1+d)=40∴d=3(2)a20,a21,a22,…,a30首项为a20,公差为d2∴a30=...