23. “Oh, really?” the mother ___ what to say, so she started to unload the dishwasher. “Do you need any help?” She asked after a while. (NOT KNOW)

В рассказе о прошлом требуется Past Simple; отрицание образуется с did not и начальной формой глагола.

“Oh, really?” the mother did not know what to say, so she started to unload the dishwasher. “Do you need any help?” she asked after a while.

Ответ: did not know.