Usamos "at" para:

At + lugares comunes

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• At home - En casa
• At school - En la escuela
• At work - En el trabajo
• At university - En la universidad
• At the dentist's - En el dentista
• At the movies - En el cine
• At the theater - En el teatro
• At the airport - En el aeropuerto
• At the library - En la biblioteca
• At the doctor's - En el doctor
• At the bank - En el banco
• At a concert - En el concierto
• At a meeting - En la reunión
• At a party - En la fiesta
• At John's - En lo de John
• At Laura's - En lo de Laura

At + lugares específicos

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• At Madison Square Garden
• At Kennedy Airport
• At Buckingham Palace
• At the University of Florida

At + direcciones y domicilios

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• At 2354 Rivadavia Avenue
• At 3456 Belgrano Street

At + ciertas cosas o posiciones

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• At the top - En la cima / arriba de todo
• At the bottom - En el fondo / debajo de todo
• At the side - A un lado/costado
• At the front - En el frente
• At the back - En la parte de atrás
• At the end - Al final
• At the door - En la puerta
• At the window - En la ventana
• At the reception - En la recepción

Usamos "on" para:

On + superficies

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• On the floor - En el piso
• On the ceiling - En el techo
• On the table - En la mesa
• On the chair - En la silla
• On the list - En la lista
• On the map - En el mapa
• On the beach - En la playa
• On the shelf - En el estante

On + medios de transporte

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• On a ship - En un barco
• On a train - En un tren
• On a plane - En un avión
• On a bus - En un autobús
• On a bicycle - En una bicicleta
• On a motorcycle - En una motocicleta
• On a horse - A caballo
• On a ferry - En un transbordador

On + partes del cuerpo

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• On my leg - En mi pierna
• On your arm - En tu brazo
• On his shoulder - En su hombro

On + direcciones

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• On the left - A la izquierda
• On the right - A la derecha
• On the way - En el camino

On + ciertas cosas y lugares

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• On the radio - En la radio
• On television - En la TV
• On a farm - En una granja

Usamos "in" para:

In + países

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• In Argentina
• In Spain
• In Mexico

In + ciudades

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• In New York
• In Madrid
• In Mexico City

In + habitaciones

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• In the bathroom - En el baño
• In the kitchen - En la cocina
• In the bedroom - En el dormitorio

In + cuerpos de agua

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• In the sea - En el mar
• In the water - En el agua
• In a river - En un río
• In the ocean - En el océano

In + clima/tiempo

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• In the rain - En la lluvia
• In the sun - En el sol
• In the wind - En el viento
• In the fog - En la neblina

In + ciertos lugares y expresiones

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• In prison - En prisión
• In hospital - En el hospital
• In bed - En la cama
• In Oak Street - En la calle Oak
• In a line - En una cola
• In a row - En fila
• In a queue - En una cola
• In the sky - En el cielo
• In a book - En libro
• In a magazine - En una revista
• In a letter - En una carta
• In a mirror - En un espejo
• In a car - En un auto
• In a taxi - En un taxi
• In a helicopter - En un helicóptero