3 sentences

1. 历年的学校档案都保存得非常完好。

   lì​nián de xué​xiào dàng'àn dōu bǎo​cún de fēi​cháng wán​hǎo.

   School archives from over the years have been perfectly preserved.

   Source: Dong Chinese Dictionary

2. 历年累积下来的工作经验对他很有帮助。

   lì​nián lěi​jī xià​lai de gōng​zuò jīng​yàn duì tā hěn yǒu bāng​zhù.

   The work experience he accumulated over the years has been very helpful to him.

   Source: Dong Chinese Dictionary

3. 历年考题的难度都保持在相对稳定的水平。

   lì​nián kǎo​tí de nán​dù dōu bǎo​chí zài xiāng​duì wěn​dìng de shuǐ​píng.

   The difficulty of the exam questions over the years has remained relatively stable.

   Source: Dong Chinese Dictionary