3. Mike (spoke / was speaking) to me when his little sister (took / was taking) his book out of his schoolbag.

3. Mike spoke to me when his little sister was taking his book out of his schoolbag.

В данном предложении необходимо использовать Past Simple для действия, которое завершилось (Mike spoke to me), и Past Continuous для действия, которое происходило в определенный момент в прошлом (his little sister was taking his book out of his schoolbag).

Ответ: spoke / was taking