如图2－29：四面体A－BCD被一平面所截，截面EFGH是一个矩形， （1）求证：CD//平面EFGH； （2）求异面直线AB、CD所成的角。
After __whole day’s work, Mary decided to walk ___dog along the road by her house. A. the; the B. the; a
Yesterday I came across an interesting new book, 61. I would like to recommend here. It is 62. adventure story. The title is Voyage to an Amazing Kingdom. The publisher sai
母亲的诗（17分） ①母亲不是诗人，母亲不会写诗，但是今天，当我坐在宽敞明亮的写字楼里，打开电脑写这篇文章时，竟忽然觉得，母亲似乎写过一
下列物质中属于纯净物的是（ ）A、蒸馏水 B、矿泉水 C、自来水 D、天然水
从0,1,2,3,4,5,6中任意取出三个不同的数字作为二次函数的系数,可有多少个不同的二次函数的表达式?其中二次函数对应的曲线关于y轴对称的有多少个?
已知椭圆C1：＋＝1(a>b>0)与双曲线C2：x2－＝1 有公共的焦点，C1的一条渐近线与以C1的长轴为直径的圆相交于A，B两点．若C1 恰好将线段AB三等分，则(
Large quantities of water, as well as some other timely help including a medical team ___since the serious drought hit Yunnan Province. A. has offered
=_____ 
