Respuesta:
1) He didn't buy a new shirt
2)They didn't go shopping last Friday
3)She didn't have a bath in the morning
4)They didn't all sit down
5)He didn't ride a horse last week
6)She didn't take her temperature
7)She didn't run home
8)I didn't understand what he said.
9)We didn't go shopping
10)They didn't build a big house
11)They didn't buy a new PC
12)He didn't get a new mobile
13)He didn't make his bed
14)They didn't drink a cup of tea
15)I wasn't in Dubrovnik yesterday
Explicación:
Al hacer este tipo de oraciones al agregar el "Did" o "Didn't" al ser esta el pasado de "Do" y "Don't" se da por hecho que la oración esta en pasado por este verbo, por lo que ya no es necesario agregar el pasado al siguiente verbo.
Osea que cuando agregas un "Did" o "Didn't" el siguiente verbo lo dejas en presente
Espero haberte ayudado =))
