Two men are sitting together in an airplane.they are on a lo

Two men are sitting together in an airplane.they are on a long journey.One man is a teacher The other is a farmer.
They sit for a while,then the farmer says,”Let’s do something to pass time.Let’s each other riddles.“let‘s make the game more intersting.If we don't know the answer to a riddle,we have to pay,"says the teacher.
The farmer thinks about this for a while,then he says,"that's not fair.You are a teacher,you know more things than I do.I am just a farmer." "Yes,that's true!What do you think we should do."the teacher asks."If you don't know the answer to a riddle you pay me $ 100.If I don't know the answer to a riddle,I'll pay you $50."
The teacher thinks about this,then he says,"OK.That's fair.Who'll go first?"
"I will,"the farmer says."Here is my riddle.What has three legs when it walks,but only two legs when it flies?"
The teacher repeats the riddle,"Oh,thisis a good one.I'm afraid.I don't know the answer ."He gives the farmer $ 100,then says,"Tell me the answer.What has three legs when it walks,but only two legs when it flies?"
"I don't know,"the farmer says,and gives the teacher $ 50.
根据这个短文,出三个问题.要求难度适中.别出太简单的也别太难的.要问答题,什么填空选择的都一边儿去!好的再加50分!
那位仁兄的题不错，不过我不仅要问题还要答案耶！我等到今天晚上8点！