I completely disagree with the OP's opinion.

What is the main clause of this sentence?

My younger sister is twenty-two years old.

Sai is my best friend.

This is the best restaurant.

He encouraged us to muster courage.

He took out a loan to pay for his college tuition.

I have to retake the exam.

"Ah, how beautiful!" He exclaimed in admiration.

He built a fort on top of the mountain.