华山国际学友会在美国首都华盛顿(西五区)主持视频会议,请华山中学高中部的郑老师在演播厅给远在非洲(西一区至东三区)的同学介绍经验。下列时段中,对三方最合适的是:
A:华盛顿时间14:00~16:00
B:北京时间21:00~23:00
C:华盛顿时间2l:00~23:00
D:北京时间14:00~16:00
下列四幅气温曲线和降水量柱状图中,符合我国南方地区气候的是( )
已知四棱锥P﹣ABCD中,底面为矩形,PA⊥底面ABCD,PA=BC=1,AB=2,M为PC中点.
(Ⅰ)在图中作出平面ADM与PB的交点N,并指出点N所在位置(不要求给出理由);
(Ⅱ)在线段CD上是否存在一点E,使得直线AE与平面ADM所成角的正弦值为 1010 ,若存在,请说明点E的位置;若不存在,请说明理由;
(Ⅲ)求二面角A﹣MD﹣C的余弦值.
阅读短文,选择正确答案。
Hello, I am Peter. Yesterday was Sunday. I walked to my grandpa's home. It was his birthday. I bought (要) many fruit and a big cake in the morning. My grandpa and grandma liked them very much. My mother cooked the lunch. We had a good time.