已知点A,直线a,平面α.①A∈a,aαAα;②A∈a,a∈αA∈α;③Aa,aαAα;④A∈a,aαAα.以上表达正确的真命题的个数是( )A.0 B.1
用配方法解方程时，原方程应变形为（）。A．； B．； C．； D．。
_______ that all mountain roads were closed. A. So the dangerous weather became B. So dangerous did the weather become C. So dangerous became the weather D. The dangerous weather became so
Our environment isn’t as green and beautiful as it should be. There are steel(钢铁) monsters blocking out the sun, blowing out dangerous smoke, and letting out poisonous chemicals into riv
-----What ____ you doing when the UFD landed? -----I________ a book．A．are；was buying B．were；was buying C．was；was buying D．did；bought
化学变化多姿多彩，美丽如花．如图中甲、乙、丙、X 分别是CuO、C、CO 和HCl 中的某一种，甲、乙、丙均能与X 发生化学反应，则X 是（ ） A．CuO B．C
下列变异形成的遗传病中，不能用显微镜观察到的是（） A．21三体综合征 B． 猫叫综合征 C．镰刀型细胞贫血症 D． 苯丙酮尿
（2011年河北，36题）已知氯化钠溶液和硝酸银溶液反应生成氯化银(AgCl)沉淀和硝酸钠。为测定某生理盐水的溶质质量分数，将生理盐水样品与足量的硝
满足约束条件
，则
的最小值为_________. 