On the multiple choice, the answers Dw i'n yfed coffi yn Y Drenewydd? and Dw i'n yfed coffi yn y Drenewydd? were both considered correct. Why? Surely there's a rule for capitalisation?
AbunPang, Auleliel, and DeadFish37: writing "yn Y Drenewydd" is not a serious mistake; however, the rule (as I understand it) is: "do not capitalize 'y' in a place-name". So, "yn y Drenewydd" is the preferred spelling.
--EDIT--
I now understand that 'mewn' means a place like a garage or anywhere unspecific. Whereas 'yn' means a specific place such as Newport or Swansea.