Until 1999, the Panama Canal was controlled by whom?A) Afghanistan B) China C) the United States D) Panama

The correct answer to this question is C.  The only other
one that would make any sense at all is D.

The Panama Canal
belonged to the United States from the time that the US built it in the early 1900s. 
The US owned the canal as well as an area on both sides of the canal known as the Panama
Canal Zone.  This state of affairs continued until 1977.  At that point, Jimmy Carter
negotiated a settlement in which the canal would be given back to Panama.  Carter did
this because he wanted a foreign policy based more on idealism than on raw power.  The
handover of the canal became complete in 1999.  From then on, Panama has run the
canal.