根据句意和汉语注释，写出单词的正确形式。
(1)The ____ （建议）they have offered us are very useful, we should take them.
(2)Beijing is the capital of China, it is also the ____ （文化）center of China.
(3)Tonight, they are going to celebrate their father's ____ (四十) birthday.
(4)How beautiful those circles on those ____ (蝴蝶)wings are!
