2 sentences

1. 老师正在批改卷子。

   lǎo​shī zhèng​zài pī​gǎi juàn​zi.

   The teacher is grading the exam papers.

   Source: Dong Chinese Dictionary

2. 助教正在帮教授批改作业。

   zhù​jiào zhèng​zài bāng jiào​shòu pī​gǎi zuò​yè.

   The teaching assistant is helping the professor grade assignments.

   Source: Dong Chinese Dictionary