演替过程中，灌木逐渐取代了草本植物，其主要原因是（）

如图，扇形DOE的半径为3，边长为$\sqrt{3}$的菱形OABC的顶点A，C，B分别在OD，OE，弧ED上，若把扇形DOE围成一个圆锥，则此圆锥的高为（   ）

    Mrs Smith is my teacher．At school she____us English．Her English is very good so we all like her．She has got two daughters，Gina and Helen．They are____at our school．So I know some things about them Gina____English very well．Helen is good at music．She plays the____very well．She is in the Music____．There,she and our music teacher Ms White help students with the piano．

若等腰三角形腰上的高是腰长的一半，则这个等腰三角形的底角是（ ）

下列句子中划线的词语使用恰当的一项是（    ）