7.
在平面直角坐标系中,定义\(d(P,Q)=|x_{1}-x_{2}|+|y_{1}-y_{2}|\)为两点\(P(x_{1},y_{1})\),\(Q(x_{2},y_{2})\)之间的“折线距离”\(.\)则下列命题中:
\(①\)若\(C\)点在线段\(AB\)上,则有\(d(A,C)+d(C,B)=d(A,B)\).
\(②\)若点\(A\),\(B\),\(C\)是三角形的三个顶点,则有\(d(A,C)+d(C,B) > d(A,B)\).
\(③\)到\(M(-1,0)\),\(N(1,0)\)两点的“折线距离”相等的点的轨迹是直线\(x=0\).
\(④\)若\(A\)为坐标原点,\(B\)在直线\(x+y-2 \sqrt {5}=0\)上,则\(d(A,B)\)的最小值为\(2 \sqrt {5}\).
真命题的个数为\((\) \()\)