me: good day sir!
VO: you will study physics?
me: I was admitted by the department of physics,...(be interrupted by vo)
vo: why choose US?
me: actually ,I will be working in Dr,XX（chinese） lab, which is a interdisplinary program, and no similar program are available in china now.
VO;(impatiently),every university in china have department of physics, i asked why choose US?
Me:Indeed, my specialty is use mathematical tools to solve biology questions.  i will use mathematical models to simulate and predict the protein structures instead of molecular experiments.this method will greatly shorten the period of medicine production.
Vo:(I can see "unbelieve" on his face)what is your plan when you graduate?
me:i will apply this simulation method in china ,I want to go to chinese center for disease control and prevention. the method i will learn will help biologist to found effective medicine for deadly disease such as SARS.
Vo: your can use physics to cure SARS?(wave his head)
Me:this simulation method is a new growpoint in this area, and chinese government also give 1 billion RMB to this china CDC this year.
Vo: i don't know why how to use physics to cure SARS?
Me: I was be working in a bioengeering lab. you can see my offer letter, my  professor is from bioengeering. (I want show him the offer letter and the  webpage of my professor).you can see that dr XX give me fully financial support and here is what he is working on.(about your research area on the webpage.but he  didn't take a look)
VO:(using his computer without a word and glance at me)
Me:I was confused at first when i receive the I20, I asked my professor, and  found that if I was admitted by this program, i have to be admitted by the Department of physics since this lab is under the physics department.
Vo:if you are confused ,i am also confused.
Me: I am very clear(I was nervous now)now, since your can see from drXX's page (show him the page of web again,and he take it this time)
Vo: (take the paper to another visa officer and come back in 20 seconds)I can believe you, he didn't come back and you won't come back too.(point on the the chinese professor's curriculum vita on the page).
Me: you know when dr XX finished his study ten years ago,china government give nothing to his  field ,he had to continue his research in US. and it is different now.
Vo:if i give you the visa ,you won't come back.(the "received" is already on  the passport).
Me...(pick up the visa)
I have to say, from the first sentence, the decision has been made. he was just looking for a "reasonable" reason in the following words.