题干

抛物线y=ax2+bx+c的图象如图,则下列结论:①abc>0;②a+b+c=2;③4a-2b+c<0;④b2-4ac>0.其中正确的结论是 (     )

A:①②

B:②③④

C:②④

D:③④

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答案(点此获取答案解析)

C

同类题1

阅读下面的文言文,完成文后各题。

游丹霞记

【清】袁枚

    甲辰春暮,余至东粤,闻仁化有丹霞之胜,遂泊五马峰下,另买小舟,沿江往探。山皆突起平地,有横皴,无直理,一层至千万层,箍围不断。疑岭南近海多螺蚌,故峰形亦作螺纹耶?尤奇者,左窗相见,别矣,右窗又来;前舱相见,别矣,后舱又来。山追客耶,客恋山耶?舛午惝恍,不可思议。

    行一日夜,至丹霞。但见绝壁无蹊径,惟山胁裂一缝如斜锯开。人侧身入,良久得路。攀铁索升,别一天地。借松根作坡级,天然高下,绝不滑履;无级处则凿崖石而为之,细数得三百级。到阑天门最隘,仅容一客,上横铁板为启闭,一夫持矛,鸟飞不上。山上殿宇甚固甚宏阔,凿崖作沟,引水僧厨,甚巧。有僧塔在悬崖下,崖张高幂吞覆之。其前群岭环拱,如万国侯伯执玉帛来朝,有豪牛丑犀,犁靬幻人,鸱张蛮舞者。

    余宿静观楼。山千仞衔窗立,压人魂魄,梦亦觉重。山腹陷进数丈,珠泉滴空,枕席间琮琤不断,池多文鱼在泳游。余置笔砚坐片时,不知有世,不知有家,亦不知此是何所

    次日,循原路下,如旧书,愈觉味得。立高处望自家来踪,从江口到此,蛇蟠蚓屈,纵横无穷,约百里而遥。倘用郑康成虚空鸟道之说,拉直线行,五马峰至丹霞,片刻可到。始知造物者故意顿挫作态,文章非曲不为工也。第俯视太陡,不能无悸,坐石磴而移足焉。

    僧问丹霞较罗浮何如?余曰:罗浮散漫,得一佳处不偿劳,丹霞遒景胜矣。又问:“无古碑何也?”曰:雁宕开自南宋,故无唐人题名;黄山开自前明,故无宋人题名;丹霞为国初所开,故并明碑无有。大抵禹迹至今四千馀年,名山大川,尚有屯蒙未辟者,如黄河之源,元始探得,此其证也。然即此以观,山尚如此,愈知圣人经义更无津。若因前贤偶施疏解,而遽欲矜矜然阑禁后人,不许再参一说者,矣妄矣,殆不然矣。

同类题5

阅读下列短文,从每题所给的四个选项(A、B、C和D)中选出最佳选项。

    Ongoing conflicts across the Middle East have prevented more than 13 million children from attending school, according to a report published by UNICEF, the United Nations Children's Fund.

    The report states that 40% of all children across the region are currently not receiving an education, which is a result of two consequences of violence: structural damage to schools and the displacement (转移) of populations, also called “forced migration.” Both issues result from the violence that has crossed the region in recent years. The report examines nine countries where a state of war has become the ordinary state. Across these countries, violence has made 8,500 schools unusable. In certain cases, communities have relied on school buildings to function as shelters for the displaced, with up to nine families living in a single classroom in former schools across Iraq.

    The report pays particularly close attention to Syria, where a bloody civil war has displaced at least nine million people since the war began in 2011. With the crisis (危机) now in its fifth year, basic public services, including education, inside Syria have been stretched (竭尽所能) to breaking point. Within the country, the quality and availability of education depends on whether a particular region is suffering violence.

    The report concludes with an earnest request to international policymakers to offer money and other resources to help ease the regional crisis. With more than 13 million children already driven from classrooms by conflict, the educational future of a generation of children are in the balance. This is destroying the future for an entire region.