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"En" is a form of "en", a preposition which is often translated as "in". "Películas" is a form of "película", a noun which is often translated as "movie". Learn more about the difference between "en" and "películas" below.
en()
A preposition is a word that indicates the relationship between a noun and another word (e.g., He ran through the door.).
la película()
A feminine noun is almost always used with feminine articles and adjectives (e.g., la mujer bonita, la luna llena).
