—Good idea. I think ____ the general manager ___ the chief engineer have the courage to take on the challenge.
A:neither; nor
B:either; or
C:both; and
D:not only; but also
下列关于有丝分裂观察的实验说法正确的是( )
已知△ABC,AB=AC=4,BC=2,点D为AB延长线上一点,BD=2,连结CD,则△BDC的面积是____,cos∠BDC=____.
如图所示,小球悬浮在水中,请在图中画出小球所受浮力和重力的示意图.