有20个自然数，它们的和是1999，在这些数里，奇数的个数比偶数的个数多，那么这些数里，偶数最多有（　　）个．

地理的两极和地磁的两极并不重合，世界上最早记述这一现象的人是我国宋代学者____ ．“郑和七下西洋”是我国古代航海史上的一项伟大壮举，这一伟大壮举的实现得力于____ 的发明．

读一读，补全对话。

A. What about you?            
B. How old is your cousin?

C. Do you have any cousins?    
D. What is his name?
 Ann: Hi! Mike.____
Mike: Yes, I have one cousin.
Ann: ____
Mike: He's 9 years old. ____
Ann: I have one cousin, too. He's a boy.
Mike: ____
Ann: His name is Dan.He is 10 years old.