Given the following passage

"The official policy of the U.S. Government is that Thailand was not an ally of the Axis, and that the United States was not at war with Thailand. The policy of the U.S. Government ever since 1945 has been to treat Thailand not as a former enemy, but rather as a country which had been forced into certain actions by Japanese blackmail, before being occupied by Japanese troops. Thailand has been treated by the United States in the same way as such other Axis-occupied countries as Belgium, Czechoslovakia, Denmark, Greece, Norway, Poland, and the Netherlands.",

answer the following question. Note that the answer is present within the text.

Question: What group took over Thailand?
the Axis
The passage discusses the role of Thailand during World War II. It states that despite having taken certain actions before being occupied by Japanese troops, Thailand was not considered an ally of the Axis and as such has been treated in a similar way to countries that were actually allies of Germany and Japan. The text mentions Belgium, Czechoslovakia, Denmark, Greece, Norway, Poland and the Netherlands; all these countries were indeed Allies but they had been invaded or otherwise forced into cooperation with Nazi Germany at some point during the war.
Given this context:
- under A we have "Thailand", which is present elsewhere in the question so it cannot be part of an answer here;  
- under B we have "Japan"; while it's true that Japanese forces occupied (partially) Thailand after.