"Yes, I went to school on Monday."

Translation: Do, mi es i i'r ysgol ddydd Llun.

[Willowfae]

Why was "Do, es i ysgol dydd Llun" not accepted? The English didn't ask for 'the school'.

[ibisc]

Welsh uses y with places we go to regularly, especially to just one of them. It is rather like English expressions such as 'I went to the pub/cinema/park/local museum, ...' but used even more widely. So:

• Es i i'r capel/eglwys/ysbyty/ysgol/dafarn/gwely....

[Willowfae]

But the English sentence is just asking about going to school not a specific school

[ibisc]

That makes no difference to the Welsh pattern. The two languages work in different ways.

[integra1]

I left out the "mi" and it was not accepted. Why is it mandatory here?

[ibisc]

Mi in this pattern is never mandatory. The version Do, es i i'r ysgol ddydd Llun is one of the accepted alternative answers.