Oscar says he ___ the washing-up after dinner.  will do is doing

The correct answer is "will do."

In this context, Oscar is making a statement about an action he intends to perform in the future, specifically after dinner. The phrase "will do" conveys a future intention, indicating that Oscar is willing to take on the responsibility of doing the washing-up.

On the other hand, "is doing" suggests that the action is currently in progress. Using "is doing" would imply that Oscar is already in the midst of washing the dishes at the moment of speaking, which does not align with the context of the statement that refers to a future task following dinner.

Thus, the most appropriate choice is "will do," as it properly reflects his intention regarding the washing-up after dinner.