He was too excited _________. [ ]
A. speak
B. to speak
C. not to speak
D. speaking
答案:B
已知四边形ABCD的两条对角线AC与BD互相垂直,则下列结论正确的是
A.当AC=BD时,四边形ABCD是矩形
B.当AB=AD,CB=CD时,四边形ABCD是菱形
C.当AB=AD=BC时,四边形ABCD是菱形
D.当AC=BD,AD=AB时,四边形ABCD是正方形
A.+→
B.→+
C.+→
D.→+