I'd appreciate_____if you could come and help me once more and I always appreciate_____me with my English in the past.
A:this; you to help
B:that;you helping
C:it;you to help
D:it;your helping
如图,O为矩形ABCD对角线的交点,DE∥AC,CE∥BD.
(1)求证:四边形OCED是菱形;
(2)若AB=3,BC=4,求四边形OCED的面积.
如图所示的实验装置中,极板A接地,平行板电容器的极板B与一个灵敏的静电计相接.将A极板向左移动,增大电容器两极板间的距离时,电容器所带的电量Q、电容C、两极间的电压U,电容器两极板间的场强E的变化情况是( )