2 sentences for 中线 (zhōng​xiàn)

1. 三角形的三条中线交于其重心。

   sān​jiǎo​xíng de sān tiáo zhōng​xiàn jiāo yú qí zhòng​xīn.

   The three medians of a triangle intersect at its centroid.

   Source: Dong Chinese Dictionary

2. 足球比赛开球时，双方球员必须站在中线两侧。

   zú​qiú bǐ​sài kāi​qiú shí, shuāng​fāng qiú​yuán bì​xū zhàn zài zhōng​xiàn liǎng cè.

   At the kickoff of a football match, players from both sides must stand on either side of the halfway line.

   Source: Dong Chinese Dictionary