题目

Some years ago,on a hot summer day,a little boy decided to go swimming in the river near his house. He _____ into the river. He swam and swam._____ he didn't find he was swimming towards the middle of the river and there was an alligator(鳄鱼)in the river. His mother in the house _____ out of the window and saw the two getting closer and closer. She ran towards the river _____ and shouted at her son as loudly as she could. The little boy heard his _____ voice and swam back to his mother. But it was too _____,Just as he reached her,the alligator _____ him. The mother caught her little boy by 某实心长方体，质量是1.08kg，它的长、宽、高各为40cm、10cm、1cm．（ρ铝=2.7×103kg/m3，ρ铅=11.3×103kg/m3，ρ铜=8.9×103kg/m3，ρ铁=7.9×103kg/m3）制成这物体的材料是A.铅B.铜C.铁D.铝