Réponse :

Bonjour,

I/

a)He saw the ghost while he was going upstairs.

b) Their car suddenly stopped while they were driving.

c) While she was walking to school she met a ghost.

d) I was sleeping when suddenly I heard  strange noises in my bedroom.

d) My friends and I were staying in an old castle when we met a ghost.

II/

a. I was waiting the bus when a vampire kidnapped me.

b. we were eating pancakes when we heard a loud « bang » upstairs.

c. She was watching a movie in my room when the lights went out.

d. Jack and Tom were playing football when they saw a huge shadow.

e. Rose and I were walking home when it started to rain.

Explications :

Prétérit "be" + ing :

=  Sujet   +  was / were +  base verbale - ing