开创于北魏孝文帝时期的石窟是()
A.莫高窟
B.龙门石窟
C.麦积山石窟
D.云岗石窟
参考答案:D
— John failed his final exam.
— I'm not surprised at the news ______. ______, he is never seen busy with his lessons. [ ]
A. at all, After all
B. in all, After all
C. above all, In all
D. at all, In all
如图所示,质量分别为m1、m2的两个物体通过轻弹簧连接,在力F的作用下一起沿水平方向做匀加速直线运动(m1在光滑地面上,m2在空中),力F与水平方向的夹角为θ.则m1的加速度大小为( )
A.Fcosθm1
B.Fsinθm2
C.Fsinθm1+m2
D.Fcosθm1+m2