某学者曾做过如图a所示的实验,即在天竺葵的同一叶片的不同部位分别滴加一定浓度的生长素溶液、水和14C葡萄糖,待充分作用后,得到如图b所示的
定义运算,如果复数满足,那么复数对应的点位于坐标平面的第( )象限 A、1 B、2 C、3 D
设异面直线a与b所成的角为50°,O为空间一定点,试讨论,过点O与a、b所成的角都是θ(0°≤θ≤90°)的直线l有且仅有几条?
牛奶中含有乳球蛋白和酪蛋白等物质,在奶牛的乳腺细胞中,与上述物质的合成有密切关系的细胞结构是 A.线粒体、内质网、中心体、高尔基体 B.线
He has made _________ progress that all of us want to learn from him. A. such a good B. such good C. a so good D. such good
Bush, 59, looked fresh and _______ as he _______ of the sunny weather to enjoy one of his favorite pastimes. A. energetic; took advantage B. cautious; took charge C. outgoing
已知向量,.若向量满足,,则( ) A. B. C. D.
下图表示世界能源消费构成的变化,据此判断7~8题。7.图中①、②、③、④代表的能源,依次是( ) A.煤、石油、天然气、水电和核电 B.石油、天