1. Wen Dave arrived/was arriving home,his mother was/were making the dinner 2. When I did /was doing my homework I did listen /was listening to some music
3.The participant was / were answering a question when the show end/ended​

ответ: 1. ...arrivedwas making...

2. ...did...was listening...

3. ...was answeringended...

Объяснение:

В 1м предложении past simple, п.ч. есть временное слово when, затем past continuous в ед. числе.

Во 2м и 3м предложении тот же принцип