Alkenes play a very important role in organic chemistry.

Mr. Zhai is my best friend.

He is a famous composer.

He cautioned not to speak ill of others, saying, 'Illness enters by the mouth, and disaster does not come out of it.'

He is truly demonstrating talent that surpasses his master, just as the saying 'the student has surpassed his or her teacher' goes.

He was my student, but now he has become so proficient that it can be said 'the student has surpassed his teacher.'

He checked whether he remembered or not.

The ship sank into the sea.

My mother woke me up.

My new keyboard makes typing very enjoyable.