There are two river Dees that I know of. One flows through Chester and out into the Irish sea south of the Mersey, so Chester should be an acceptable answer. For the Thames, not only Oxford but what about Reading? The Severn flows through Gloucester (which you accept) and also Worcester. The Mersey flows through S. Manchester too.
So, there is a flaw in this quiz. Wouldn't it be better to name the cities and ask us to state the rivers?
So, there is a flaw in this quiz. Wouldn't it be better to name the cities and ask us to state the rivers?