3 sentences

1. 他在大学主修的是理学。

   tā zài dà​xué zhǔ​xiū de shì lǐ​xué.

   He majored in science at university.

   Source: Dong Chinese Dictionary

2. 他在大学毕业时获得了理学学士学位。

   tā zài dà​xué bì​yè shí huò​dé le lǐ​xué xué​shì xué​wèi.

   He received a Bachelor of Science degree when he graduated from university.

   Source: Dong Chinese Dictionary

3. 朱熹是理学的主要代表人物。

   Zhū Xī shì Lǐ​xué de zhǔ​yào dài​biǎo rén​wù.

   Zhu Xi is the main representative of Neo-Confucianism.

   Source: Dong Chinese Dictionary