Dear Smiths,
Here and now I'd like to extend my thanks to you all for your help and considerate care.
During these two weeks I study in your beautiful school, all of your family members have given me so much care: helped me with my English: furthermore, arranged for special activities to let me experience a different culture. You have done too much for me.
I'll remember you forever, and look forward to your trip to China and give me a chance to help you in return.