The SI system is a standard unit system used worldwide.

My uncle is a famous zoologist.

He is a world-renowned ichthyologist.

I use a tram for commuting every day.

My brother is a famous biologist.

It is rumored that he is a member of a secret society.

He has wanted to become a superhero since he was a child.

I met him for the first time in a long time.

The afternoon classes are more difficult than the morning classes.

No, that is incorrect.