古典问题：有一对兔子，从出生后第3个月起每个月都生一对兔子，小兔子长到第三个月 　　　后每个月又生一对兔子，假如兔子都不死，问每个月的兔子总数为多少？-Classical problem: There is one pair of rabbits, from the first three months after the birth of every month from birth to a pair of rabbits, bunnies grow up to the third mo