6. In the same Cartesian coordinate system, there are infinitely many lines with the expression $y=k x+b(k, b$ being real numbers, $k \neq 0)$, (they form a family of lines). Among these lines, no matter how they are selected, it must be ensured that at least two lines pass through exactly the same quadrants. The minimum number of lines that need to be selected is
A. 4 lines
B. 5 lines
C. 6 lines
D. 7 lines
6. $\mathrm{D}$ Hint: Classify by the quadrant the line is in, there are 6 categories. When $k>0$, $\left\{\begin{array}{l}b>0 \\ b=0 ; k>0 \\ b<0 . \text { By the pigeonhole principle, at least } \\ b=0\end{array}\right.$ 7 lines need to be drawn.