若以$\left(\begin{array}{c}\begin{array}{ccc}1& a& 3\end{array}\\ \begin{array}{ccc}a& 4& 1\end{array}\end{array}\right)$为增广矩阵的线性方程组有唯一一组解，则实数a的取值范围为____ ．

    Look, this is my city. There are many bikes and buses on the streets. Let's count. There are ____  bikes and ____  buses. Look here, there are also ____   taxis and ____  cars. My city is big and beautiful!

假设在时间间隔T内的任何时刻，两条不相关的短信机会均等地进入同一台手机.若这两条短信进入手机的间隔时间不大于$t\left(0<t<T\right)$，则手机受到干扰.手机受到干扰的概率是(      )

如图，BD、CE相交于点A，下列条件中，能推得DE∥BC的条件是（　　）