—Yes, isn't it? I ________ such a great one before!
A：never saw
B：had never seen
C：never see
D：have never seen
空气水平运动的直接原因是 ( )
下列命题：①对角线相等的菱形是正方形；②对角线相等且互相垂直平分的四边形是正方形；③一组邻边相等且对角线相等的平行四边形是正方形；④四边都相等，四角都相等的四边形是正方形.其中命题正确的有（）
