1、【题目】设数列 {an} 的前 n 项和为 Sn,则 {an} 等差。
(1) S n4=n 2+2n, n=1,2,3
(2) S n4=n 2+ 2n +1,n=1,2,3
选项:
A.条件(1)充分,但条件(2)不充分.
B.条件(2)充分,但条件(1)不充分.
C.条件(1)和(2)单独都不充分,但条件(1)和条件(2)联合起来充分.
D.条件(1)充分,条件(2)也充分.
E.条件(1)和(2)单独都不充分,但条件(1)和条件(2)联合起来也不充分.
答案:
A
解析:
等差数列的前n项和公式为Sn=An2+Bn,A、B为全体实数,因此条件(1)充分,条件(2)不充分,选A。
1、【题目】About20ofthepassengerswhowereinjuredinaplanecrasharesaidtobein_____condition.
选项:
A.decisive
B.urgent
C.vita
D.critical
答案:
解析:
1、【题目】The opportunity to explore and play and the encouragement to do so Can ________the performance of many children .
选项:
A.withhold
B.prevent
C.enhance
D.justify
答案:
C
解析:
暂无解析
1、【题目】In 1991,while t11e economies of industrialized countries met an economic_____,the economies of developing countries were growing very fast .
选项:
A.reviva
B.repression
C.recession
D.recovery
答案:
C
解析:
暂无解析
1、【题目】Many _______will be opened up in the future for those with a university education .
选项:
A.probabilities
B.realities
C.necessities
D.opportunities
答案:
D
解析:
暂无解析
1、【题目】The poor countries are extremely _______to international economic fluctuations
选项:
A.inclined
B.vulnerable
C.attracted
D.reduced
答案:
B
解析:
暂无解析
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