题目内容：

六年级寒假乐园（福建教育出版社）
40页的IQ小博士,10,14,24的益智乐园
IQ小博士:There is a duck in front of two ducks.
There is a duck between two ducks.
There is a duckbehind two ducks.
How many ducks are there?
There are__________