过点(-1,0)作抛物线y=x2+x+1的切线,则其中一条切线为( ) A.2x+y+2=0 B.3x-y+3=0C.x+y+1=0 D.x-y
已知:在如图1所示的平面直角坐标系xOy中,A,C两点的坐标分别为,(其中n>0),点B在x轴的正半轴上.动点P从点O出发,在四边形OABC的边上依次沿O—
The teacher told me that the students I wanted to see were seen___ football on the playground just now. A playing B to be playing C play D to play
下列叙述中正确的是( ) A.共价化合物中原子都一定满足最外层8电子结构 B.通过共价键形成的分子一定是共价化合物 C.共价化合物中可能含有
In our school students are _____ according to how much they know and how old they are. A.classified B.combined C.condemned D.betrayed
“达菲”是预防甲型H1N1流感的有效药物,其主要成分是莽草酸(C7H10O5).请计算: (1)莽草酸中C、H、O元素的质量比: . (2)莽草酸中氧元素的质
No potatoes for me—I’m _______ a diet. A. at B. in C. on D. with
下列各句中划线的词不属于古今异义的一项是( ) A.约为婚姻 B.备他盗出入与非常也 C.财物无所取 D.沛