唐朝的繁盛吸引了世界各地的人们漂洋过海、不远万里来到中国，唐帝国自身也以博大的胸怀兼容并蓄外来文化的精华，中外文化双向交流、共享繁荣，下列事件能佐证这一现象的是（    ）

①和亲结盟    ②鉴真东渡    ③玄奘西行    ④遣唐使来访

近年来，有学者通过计量化的统计得出，从武汉失守到太平洋战争爆发期间，国民党正面战场组织了南昌会战等9次大规模战役，占国民党22次会战的41%，甚至有过一些攻势作战，难能可贵。这一时期国民党还有大的战斗496次，占整个抗战时期战斗的44%，共伤亡137.6万人，占整个抗战时期伤亡人数的43%。由此最能说明（     ）

若a，b，c是常数，则“ a>0 ，且b²-4ac<0 ”是“对任意 $x\in R$ ，有ax²+bx+c>0 ”的(    )

   Why do we come to school? Most of us may say we come to school to study. But to study needs a right way, or you either waste the time or the money. The following are the ways for studying.
    The best time for reading is morning. In the morning the air is fresh and the mind is clear. For that reason we can get good results.
In studying we must have patience（耐心）. If we have not known a text well, we must read it again. We should not read the next one until we have learned the first one well.
   When we are studying, we must put our hearts into the books, or we can get nothing from the books while we are reading.
We must always ask “whys”. If it is not well understood, write it down and ask our teachers or our parents, brothers or friends. In any possible way, we must know it completely and what we have learned can be used well and made better.
   Though there are many ways for studying, yet what I have said above will be enough if we can keep them in heart and do so.