我国最重要的内河航线是（），南北方向的重要内河航线是（）。

     Carol and Susan were great friends. They were in the same class at __1__ , and they often played together after school. When Carol was eight years __2__ , her mother had a baby. Carol was __3__ , to have a little sister. She always talked about her to __4__ . Susan had no brothers or sisters. At first Susan liked listening to her, __5__ , after a few days she didn't liked her to talk about it. One morning when the two __6__ , were on their way to school, Carol __7__ , Susan, "Do you know, Susan, my baby __8__ , got half a kilo in weight(重量) this week?"
     "That' not very much." answered Susan. "I know a __9__ . It gets five kilos a day."
     "Oh, that can't be true!" answered Carol. " __10_ , baby is it?" "An elephant's," said Susan.