泰国的签证有几种？
1. 非移民类B2签证 B-2 visas are for nonimmigrant visitors to the United States for pleasure or medical treatment. You cannot work， study， get training， or perform volunteer service in the U.S. on a B2 visa.
2. 过境签证 G visa is for travelers who have a valid flight itinerary that requires them to transit through an airport within the United States but whose final destination is outside the country and they don't need a visa to travel to their ultimate destinations. For example， if you live in China and go visit your friend who lives in France by first going via New York where you will only be there for less than 24 hours before continuing onward to Paris. In this case， you might be eligible for a G visa. Note： A G visa does not authorize any kind of employment while you're in US but it allows you to explore the city and its surrounding areas with no limitations up to 90 days maximum period. To apply for a G Visa， you must meet all these conditions：
·You can enter the USA without a visa as long as they allow travelers to stay for no more than 90 days; however， please check whether your point of entry meets those requirements because some airports do not accept G visa holders；
·The purpose of your trip to the USA must be one of the following： tourist， business， visiting friends or relatives (visiting a relative would be allowed even though he/she isn’t American citizen)；
·Transit（if applicable） should take place directly from one connecting flight to another， i.e.， you shouldn't spend too much time at the airport；
3. 移民类签证 Immigration visas， also called immigrant visas， let applicants become permanent residents (“green card” holder) after entering the United States. An applicant may get either a non-quota or quota immigration visa.
There are two types of immigration visas：
(a) Non-quota Immigrant Visas： All immigrants admitted under “parole” are considered to be non-quota immigrants. Parole was originally used when the government could find individuals who had already entered illegally， such as people fleeing persecution． It now refers to allowing foreign nationals to temporarily enter the United States on certain circumstances specified by the president and approved by the secretary of Homeland Security. There are currently three categories of parolees：
i. Special