Alkenes play a very important role in organic chemistry.

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.

He is not an ordinary human.

He planed the wood and made a model airplane.

He couldn't hide his jealousy towards her success.

He picked up the whip and started practicing.

He alienated his friends with his behavior.

He was playing with the children.

I heard that my ancestors were samurai.

He and I compete in tennis every week.