Why is 2004 a special year? Because it is a Leap Year（闰年）.

　　What's so special about that? Well, we have a Leap Year every four years. And it has 366 days, not the usual（通常）365. In a Leap Year, we have 29 days in February, while in a usual year we have only 28 days.

　　Why do we have a Leap Year? We have a Leap Year so we can keep the calendar（日历）in step（一致）with the seasons. The calendar is a kind of clock for the year. But how long is a year? A calendar year is 365 days. But a true year is 365 days, 5 hours, 48 minutes and 46 seconds long. That's the time it takes the earth to go around the sun. So every four years we have one more day, and we put it at the end of February, he shortest month of a year. Then we have a Leap Year.

A．Every year.

B．Every February.

C．Every four years.

A．for the year

B．for Leap Year

C．for the usual year

A．a day

B．a year

C．a little longer than 365 days