The jiraffes eat leaves.
Wrong
Tip: In plural and general sense do not use "the"
My brother is ___ mountain climber; he has climbed ___ Mount Everest.
My brother is a mountain climber; he has climbed the Mount Everest.
People don't take concious of the pollution problem.
Correct!
The students of the university live in the campus.
Correct!
___ Hague is ___ city in ___ Netherlands.
Hague is a city in the Netherlands.
I saw the incredible bird near the Tahoe lake.
Wrong!
Tip: Indefinite "an incredible"
___ Dominican Republic is on ___ island in ___ Caribbean.
Dominican Republic is on an island in the Caribbean.
The children are really happy when they play with their parents.
Wrong
Tip: Children is a plural noun and it has a general sense.