Alkynes play an important role in organic chemistry.

Alkenes play an important role in organic chemistry.

Alkenes play an important role in organic chemistry.

Alkanes are basic components of organic chemistry.

He is studying the history of African Americans.

The parasympathetic nervous system helps our body to relax and conserve energy.

This ancient proverb, 'know the other side and yourself, and you will not be in danger in a hundred battles', teaches us the importance of understanding ourselves and others.