gnuplot行类型不希望被更改

你能帮我吗？我希望将一行类型更改为点线.我使用这些命令:

gnuplot> set terminal png size 750,210 nocrop butt font "/usr/share/fonts/truetype/ttf-liberation/LiberationSans-Regular.ttf" 8
gnuplot> set output "/root/data.png"
gnuplot> set xdata time
gnuplot> set timefmt "%Y-%m-%d"
gnuplot> set format x "%b %d"
gnuplot> set ylabel "item1"
gnuplot> set y2label "item2"
gnuplot> set y2tics
gnuplot> set datafile separator "|"
gnuplot> plot "/root/results.txt" using 1:2 title "item1" w lines lt 4, "/root/results.txt" using 1:3 title "item2" with lines

但我总是得到洋红色线.我使用了版本4.6 patchlevel 0.感谢您的回复.