青春期性发育主要是指（）。

A.月经来潮至经期规则

B.第二性征开始发育至完成

C.产生性激素，开始对异性发生兴趣

D.性器官及功能开始发育至成熟

E.从无生育功能到有生育功能

根据句意和汉语注释，写出单词的正确形式。

小题1:The _____________ （建议）they have offered us are very useful,we should take them.

小题2:Beijing is the capital of China,it is also the _______________（文化）center of China.

小题3:Tonight, they are going to celebrate their father’s _____________ (四十) birthday.

小题4:How beautiful those circles on those ________________________ (蝴蝶)wings are!