Bonjour,

Réponse :

He was smoking a pipe when Inspector Lestrade knocked at his door.

Dr. Watson was analyzing the crime scene when the police took the body away from the crime scene

I was thinking about the case this morning and I realized that I was wrong from the start.

Sherlock and Watson were relaxing while Inspector  Lestrade was trying to solve a very difficult case.

Explications :

prétérit simple ( verbes réguliers : Base verbale-ed // verbes irréguliers par coeur )

prétérit Be-ing ( was/were + Base verbale-ing )