若A为6阶方阵,齐次方程组Ax=0基础解系中解向量的个数为2, 则
( )。\n \n \n \n \n \n \n
\n \n \n \n A.\n 2\n
\n \n\n \n \n \n B.\n 3\n
\n \n\n \n \n \n C.\n 4\n
\n \n\n \n \n \n D.\n 5\n