设(I)计算行列式A；(II)当实数a为何值时，方程组有无穷多解，并求其通解
ShegotajobasanassistantstagemanagerattheCambridgeArtsFestivalTheatre,thinkingthatitmight________toacareerasaplaywright(剧作家).
Takeit______.Itisnothingbutajoke.
________withthesizeofthewholeearth,thehighestmountainsdonotseemhighatall.
设A为3阶矩阵，|A|=3，*A为A伴随矩阵，若交换A的第1行与第2行得矩阵B，则|BA|=（）
