There are ________ approaches to English teaching. But not all of them are equally efficient for our Chinese students.
A:variety
B:accurate
C:original
D:diverse
通常不属于连续细胞系特点的是
如图所示,电源电动势为E,内阻r=R,定值电阻R1和R2的阻值均为R.平行板电容器接在R2两端,两极板长度和距离均为d,足够大屏幕与电容器右端距离为d,OO1为电容器中心轴线.一个不计重力、质量为m、电荷量为q的带正电粒子从O点以一定的初速度沿OO1方向射入电场,离开电场时的位置与电容器下极板的距离为 d4 .
西北地区利用黄河水灌溉农业区有( )