颈部淋巴干()
A.位于颈部左侧
B.位于颈部右侧
C.仅收集部分胸部及上腹部的淋巴管
D.收集部分下腹部的淋巴管
E.收集头颈部及部分胸部及上腹部的淋巴管
参考答案:B, E
在光滑水平面内有Oxy坐标系,质量m="0.25" kg的小球正沿y轴正方向匀速运动,其速度为v0=2m/s,如图所示,当质点运动到原点O处时开始受到+x方向的恒力F作用,小球恰能经过坐标为(4m,4m)的P点.求:
(1)恒力F的大小?
(2)小球经过P点时的动能大小EP=?
The discovery of a new type of ceratopsian dinosaur suggests ceratopsians ______.
A.migrated to North America around 70 -- 80 million years ago
B.arrived in Asia from North America about 90 million years ago
C.originated in Asia and later migrated to North,America
D.could have moved to Asia from North America long ago