设计师在图纸上画了一条中线，以保持对称。

The designer drew a ___mid-line on the blueprint to maintain symmetry.

足球比赛中，球必须越过中线才能开始进攻。

In soccer, the ball must cross the ___midfield line to start an attack.

在排版时，确保所有字母都对齐中线很重要。

In typography, it's important to align all letters to the ___mid-line.