如图是正常人肾小管内某种物质的含量变化曲线示意图，该物质是（　　）

请写出我国古代四大文学名著。

—How long ago _________ you _________ the English Club?
—I _________ it since two years ago.

(A)

    China Youth says that more and more girl students have entered colleges to study in the recent few years. As we know, once the number of boys was larger than that of girls, and boys did much better than girls in our country for a long time. Now, things have changed a lot.

    In recent years, the proportion of girl students is growing fast. In 1998, about 39.7% of college students were girls. In 2000, it was 41.07% and in 2001, the number was 42.14%.

    There are several reasons for this.

    Firstly, there is little difference between boys and girls in their intelligence(智力). That's to say, girls are as clever as boys. And boys have more interests than girls, so they may not always do well in their study.

    Secondly, girls are more careful than boys. They work harder at school and they do better in all exams. Another reason is that with the development of society, people pay more and more attention to girls' education.

咏雪

    谢太傅寒雪日内集，与儿女讲论文义。俄而雪骤，公欣然曰：“白雪纷纷何所似？”兄子胡儿曰：“撒盐空中差可拟。”兄女曰：“未若柳絮因风起。”公大笑乐。即公大兄无奕女，左将军王凝之妻也。

陈太丘与友期

    陈太丘与友期行，期日中，过中不至，太丘舍去。去后乃至。元方时年七岁，门外戏。客问元方：“尊君在不？”答曰：“待君久不至，已去。”友人便怒曰：“非人哉！与人期行，相委而去。”元方曰：“君与家君期日中，日中不至，则是无信；对子骂父，则是无礼。”友人惭，下车引之。元方入门不顾。