焦点在x轴上的双曲线C的左焦点为F，右顶点为A，若线段FA的中垂线与双曲线C有公共点，则双曲线C的离心率的取值范围是
如图，三棱柱ABC－A1B1C1中，侧棱AA1⊥底面ABC，AC =BC，D、E、 F分别为棱AB、BC、A1C1的中点。 （1）证明：平面A1CD； （2）证明：平面A1CD⊥平面ABB1 A1
_______was known to us all that Johnson had broken his promise _______ he would give each of us a small gift. A. As ; which B. What ; that C. It ; that D. It ; which
It’s his laziness that ________ his failure in the last exam. A. resulted from B. resulted in C. led into D. brought in
材料一，2008年是改革开放30年、真理标准问题讨论30年。 1978年5月11日,《光明日报》以“特约评论员”的名义发表了题为《实践是检验真理的唯一标准》
对下列各地区环境问题叙述不正确的是( ) A. 西北草原退化 B. 东北草原土壤酸化 C. 华北平原土壤盐渍化
--- May I open the window? It's too hot here. --- ______. A.It's your turn B.You've got it C.Go ahead D.Hold on!
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