What is the main clause of this sentence?

I feel that my lymph nodes are swollen.

Qingming Festival is a day to clean the ancestors' graves and show respect.

This text is organized using section signs.

Prepositions are an important part of grammar.

I placed the materials before the important meeting.

I had a great time with my friends at the eve festival.

An abnormality was found in the preoperative examination.

He made some preliminary statements before getting to the main topic.

Please submit this report in advance.