阅读下面短文，用括号内所给动词的适当形式填空（必要时课加情态动词或助动词）

One day while a man（44）　　（walk） on a street corner，he saw a boy selling a number of small birds in a cage（笼子）

He looked at the birds flying about in the cage and trying to get out．He（45）　　（ stand） for some time looking at the birds．At last he said to the boy，"How much do you ask for your birds？""fifty cents a bird，sir"said the boy．"I （46）　　（ not mean） how much a bird．"said the man．"But how much for all of them？I expected（47）　　（buy） them all．"

The boy began to count，and found they came to five dollars"There is your money，"said the man．The boy took it happily．Then the man opened the cage door as quickly as he could，and let all the birds fly away．

The boy，in great surprise，cried，"What did you do that for，sir？You（48）　　（ lose） all your birds．"

"I （49）　　（ tell） you why I did it，"said the man．"I （50）　　（shut） up three years in a prison（监狱），and I decided never to see anything in prison which I can make free．"