根据短文内容，从短文后的七个选项中选出能填人空白处的最佳选项。选项中有两项为多余选项。
Leap Year
Leap year is a year that has 366 days instead of the usual 365．It normally occurs every four years, always on an even-numbered year．The extra day is added to our shortest month．That is the second month of the year, which in non-leap years has 28 days, two fewer that any other month．    
Leap year is also called the bissextile year．      In our calendar system there is a need for a leap year because the solar year （the time it takes the earth to go around the sun once） is actually slightly more than 365 days long．That extra day—Feb．29 every four years—helps correct the difference between our calendar and the solar calendar．
Leap year was first made part of the calendar by the ancient Roman leader Julius Caesar．His astronomers had calculated the length of the solar year to be 365 days and six hours．So Caesar declared that an extra day be added to the calendar．    
Caesar’s adjustment, however, was not entirely accurate because his astronomers’ year exceeded the true solar year by eleven minutes and fourteen seconds．By 1582, a difference of ten days had developed between the calendar year and the true solar year．To correct this error, Pope Gregory XIII ruled that every fourth year would continue to be a leap year except for century years that could not be divided evenly by 400．By this system, century years such as 1700, 1800, and 1900 were not leap years, but the year 2000 was a leap year．  
Persons born on Feb．29 celebrate their growing up a little differently from the rest of us．     But if they go strictly by the calendar, they have only one-fourth as many birthday celebrations as most people．
A．This is done every four years．
B．This is its formal, or scientific title．
C．This may seem complicated, but it works．
D．They acknowledge that they get older each year．
E．The leap year was introduced in the Julian calendar in 46 BC．
F．When you see Feb．29 on a calendar, you know that year is a leap year．
G．In a leap year, the extra day is added to the second month, giving it 29 instead of the usual 28 days