In exercises relevant to the 'Weather' unit, sut is followed by oedd (e.g. sut oedd y tiwydd? ), which I thought was a fixed phonetic rule.
Now I'm a bit puzzled...
Can sut oedd and sut roedd be used one for the other? The 'Tips and Notes' section of the unit does not mention under what condition roedd changes into oed .
Thank you for clarifying.