to indicate the time (hour) of day
a
to refer to a specific period of the day or night when telling time
de
after the superlative to express of or in (comparison)
de
to refer to a definite place
en
after verbs of motion, when followed by an infinitive, noun, or pronoun
a
after empezar, comenzar, enseñar, aprender and ir
a
to describe personal physical characterisitcs
de
as a synonym for sobre (on)
en
as a synonym for sobre or acerca de (abour)
de
after the verb llegar
a
before a direct object pronoun that refers to a person
a
to indicate means of transportation
en