4. Susan was cutting her finger while she was slicing the bread. Choices: cut / were cutting; sliced / were slicing.

Перевод задания: Простое прошедшее или прошедшее длительное время.

Susan cut her finger while she was slicing the bread.
Сьюзан порезала палец, пока нарезала хлеб.

Короткое событие — cut (Past Simple); действие, на фоне которого оно произошло, — was slicing (Past Continuous). Слово cut в Past Simple не меняет форму.