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!
