(10分)将1.52g铜镁合金完全溶解于50.0mL密度为1.40g/mL、质量分数为63.0%的浓硝酸中，得到NO₂和N₂O₄的混合气体1120mL (标准状况)，向反应后的溶液中加入1.00mol/LNaOH溶液,当金属离子全部沉淀时，得到2.54g沉淀。求：  

（1）浓硝酸中HNO₃的物质的量浓度。

（2）该合金中铜与镁的物质的量之比为      。

（3） NO₂和N₂O₄的混合气体中，NO₂的体积分数是           。

阅读理解。

     The old man is already sixty years old. But he has only fifteen birthdays. How is it? When is his

birthday?

    Keys: His birthday is on February 29th. It’s a leap(闰年) year every four years. So he has only

fifteen birthdays.

根据短文内容填空:

1. The old man is _______ years old.  

2. He has only ________ birthdays.

3. His birthday is on _______.

4. A leap year happens(发生) every _______ years.