2 sentences

1. 前人栽树，后人乘凉。

   qián​rén zāi shù, hòu​rén chéng​liáng.

   One generation plants trees; the next enjoys the shade.

   Source: Dong Chinese Dictionary

2. 排队时请与前人保持一定的距离。

   pái​duì shí qǐng yǔ qián​rén bǎo​chí yī​dìng de jù​lí.

   Please keep a certain distance from the person in front of you while queuing.

   Source: Dong Chinese Dictionary