单项选择题The US border with Canada is the ______ in the world.
单项选择题In which countries are there programs of persuing UFO A. China and US
单项选择题If Quebec was separated from Canada, the two pacts with US ______.
单项选择题Peter Sturrock thinks that the field of UFO study is in a state of ______.
单项选择题The scientist from the French space agency did all the following things except ______.