Definite article ''de''

The definite article "de" is used in the following cases:

When the noun is plural:

de huizen (the houses)
de treinen (the trains)
de appels (the apples)

Fruits, trees, vegetables and plants:

de appel, de banana, de citroen (the apple, the banana, the lemon)
de beuk, de eik, de kastanje (the beech, the oak, the chestnut)
de prei, de wortels, de broccoli (the leek, the carrots, the broccoli)
de geranium, de tulp, de roos (the geranium, the tulip, the rose)

Professions:

de bakker (the baker)
de slager (the butcher)
de arts (the doctor)
de piloot (the pilot)

Names of rivers and mountains:

de Rijn (the Rhine)
de Theems (the Thames)
de Mont Blanc
de Kilimanjaro