Where was the ring made？It was made in Thailand.
原句正确。特定的某一件商品（物品）由某地制造，指过去发生的动作，故用一般过去时。the ring 特指这个戒指。
如果类指或泛指某种商品（物品）由某地制造，可以用一般现在时，表示现在的习惯与常态。
一般过去时的例句：
Our plate was made in China.
This one was made in America.
The machine was made in our own plant.
这台机器是我们厂自制的。《汉英大词典》
This ship was made in China.
这艘轮船是中国制造的。《汉英大词典》
The clavichord was made in Germany. 这架古钢琴是德国制造的。
Our food was made in the fast food restaurant.
我们的食物是在快餐店做的。
