Dear (điền tên bạn muốn nhé), 
I've just come back from a nice and long trip to Singapore. My first impression about this country is its cleanness. There isn't any trash on the road and at public places, this probably because of the strict rules at here. I came to many interesting places such as Marina Bay, Gardens by the Bay, and Singapore Zoo. I went their with my friends and live in low-cost hostels. Will you come with me next time.
Hope your answer soon.
Your best friend,
(tên của bạn)