单项选择题 无效婚姻是欠缺婚姻成立要件的违法婚姻。（）

未知题型 What should one do if he's got an urgent call during a meeting?A.Explain to the people present and then answer the call.B.Cut the call off at once, and apologize to the caller later.C.Answer the call before apologizing to the chairperson.D.Leave the room immediately to answer the call.

单项选择题 设观测个数为n,必要观测数为t,多余观测数为r,条件平差模型的误差方程矩阵形式为AV-W=0,其中A的维数是( ),可见方程数小于未知数的个数。 A. t×r B. n×r C. r×t D. r×n