选词填空 选择适当的词并用正确的形式填空，每词限用一次。  

                                                                                    Easy to say and hard to do

    There is ____ old man in a house. In the house there are many mice(老鼠). The old man ____ a cat. Every day the cat catches the mice and eats ____.

    One day, the old mouse says, “All mice must come to my room this evening. We must find a way to do with the cat.”

    All the mice come. Many mice speak, ____ they don't know what ____. At last, a young mouse ____ and says, “We must put a bell(铃铛) on the cat. When the cat comes ____,we can ____ the bell and run away. ____ the cat can't catch us.” “Who can put the bell on the cat?” asks the old mouse. But no one ____.

一只船在静水中的速度为3m/s，它要渡过一条河．河宽30m，水流速度4m/s．下列说法正确的是（       ）