1. 下列不等式组是一元一次不等式组的是 ()
A.$\left\{\begin{array}{l} x+2＜3,\\ x-3＞-8\end{array} \right. $
B.$\left\{\begin{array}{l} x^{2}+x＞3,\\ x-2＞0\end{array} \right. $
C.$\left\{\begin{array}{l} 3x+x＜x-1,\\ x-y＞5\end{array} \right. $
D.$\left\{\begin{array}{l} x+y＜1,\\ x-y＞1\end{array} \right. $

1. A

2. 若一个一元一次不等式组的解集在数轴上表示如图所示,则此不等式组是 ()

A.$\left\{\begin{array}{l} x≥3,\\ 2-x＞0\end{array} \right. $
B.$\left\{\begin{array}{l} x＞3,\\ x≤2\end{array} \right. $
C.$\left\{\begin{array}{l} x≤3,\\ 2-x≥0\end{array} \right. $
D.$\left\{\begin{array}{l} x＜3,\\ x-2≥0\end{array} \right. $

2. D

3. 在平面直角坐标系中,若点$P(1-2x,x-1)$在第四象限,则$x$的取值范围在数轴上表示正确的是 ()

3. A

4. 我们把$\begin{vmatrix} a&b\\ c&d\end{vmatrix} $称为二阶行列式,规定它的运算法则为$\begin{vmatrix} a&b\\ c&d\end{vmatrix} = ad-bc$,例如：$\begin{vmatrix} 1&3\\ 2&4\end{vmatrix} = 1×4-2×3= -2$,则下列结论正确的个数为 ()
①若$\begin{vmatrix} 2&3\\ 4&x\end{vmatrix} = 0$,则$x= 6$；②若$\begin{vmatrix} 2&1\\ 4&x\end{vmatrix} $＞2则$x的取值范围是x＞2$；③若正整数$m$,n满足-1＜$\begin{vmatrix} 2&m\\ n&3\end{vmatrix} $＜1,则$m+n的值为5$；④若非负数$x$,y满足 $\begin{vmatrix} x-1&y\\ 3&2\end{vmatrix}=\begin{vmatrix} x&-y\\ 3&-1\end{vmatrix} $,则实数$x$的取值范围是$x≥-2$.
A.$1$
B.$2$
C.$3$
D.$4$

4. B