4 sentences

1. 他在箱子下面铺了几层厚纸来垫底。

   tā zài xiāng​zi xià​miàn pū le jǐ céng hòu zhǐ lái diàn​dǐ.

   He lined the bottom of the box with several layers of thick paper.

   Source: Dong Chinese Dictionary

2. 他在这次模拟考试中成绩不幸垫底。

   tā zài zhè cì mó​nǐ kǎo​shì zhōng chéng​jì bù​xìng diàn​dǐ.

   Unfortunately, he finished last in this mock exam.

   Source: Dong Chinese Dictionary

3. 离晚饭还有两小时，你先吃个包子垫底。

   lí wǎn​fàn hái yǒu liǎng xiǎo​shí, nǐ xiān chī gè bāo​zi diàn​dǐ.

   Dinner is still two hours away; have a steamed bun first to tide you over.

   Source: Dong Chinese Dictionary

4. 这些基础课程是为以后的专业学习垫底。

   zhè​xiē jī​chǔ kè​chéng shì wèi yǐ​hòu de zhuān​yè xué​xí diàn​dǐ.

   These basic courses lay the foundation for future specialized studies.

   Source: Dong Chinese Dictionary