维生素和无机盐在人体中需要量虽然很少，却起着“人体运作的润滑剂”和“健康的基石”的作用，下面所列物质与缺乏症，相符的是（　　）

① Cr₂O ＋14H^＋＋6Cl^－=2Cr^3＋＋3Cl₂↑＋7H₂O

② 2Fe^2＋＋Br₂=2Fe^3＋＋2Br^－③ 2Br^－＋Cl₂= Br₂＋2Cl^－

④2Fe^3＋＋SO₂＋2H₂O=2Fe^2＋＋SO ＋4H^＋

下列有关性质的比较中正确的是(　   　)。

根据短文内容，选择方框内的单词, 并用其适当的形式填入空白处，使短文意思连贯通顺，语法正确。

Duties of a Student

    Education is the very thing that we want to receive. Our parents ____ us to school so as to enable (使能够) us to get knowledge and achieve great things in the future. The followings are the duties of a student which we should keep in ____.

    Firstly, we should be filial (孝顺的) to our parents and respectful to our ____.

    Secondly, we must study as ____ as we can.

    Thirdly, we must not tell lies.

    Last of all, we must not criticize (苛求) ____.

    To sum up, the above-mentioned rules are the very duties of a student.