3 sentences

1. 保持正确的坐姿可以减轻脊柱的压力。

   bǎo​chí zhèng​què de zuò​zī kě​yǐ jiǎn​qīng jǐ​zhù de yā​lì.

   Maintaining correct posture can reduce pressure on the spine.

   Source: Dong Chinese Dictionary

2. 长时间保持不正确的坐姿容易损伤腰椎。

   cháng​shí​jiān bǎo​chí bù zhèng​què de zuò​zī róng​yì sǔn​shāng yāo​zhuī.

   Maintaining an incorrect sitting posture for a long time can easily damage the lumbar spine.

   Source: Dong Chinese Dictionary

3. 长期保持不正确的坐姿，会对脊椎造成很大的伤害。

   cháng​qī bǎo​chí bù zhèng​què de zuò​zī, huì duì jǐ​zhuī zào​chéng hěn dà de shāng​hài.

   Maintaining poor posture for a long time can cause significant damage to the spine.

   Source: Dong Chinese Dictionary