Eve r y fall, thousands of Canada geese migrate from Canada to the eastern United

 States.  Recently, however, these geese have faced intense competition for food

 from a subspecies of Canada goose that lives year-round in the eastern United

 States.  To prevent the nonmigratory population from endangering the migratory

geese, some groups have proposed allowing hunting of the nonmigratory geese. 

 But since most hunters cannot visually distinguish the two subspecies, allowing any

 hunting is surely unwise. 

 Which of the following, if true, most seriously weakens the argument? 

A Hunting of the migratory Canada geese is permitted in some parts of Canada. 

B During the summer, only the nonmigratory geese are present in the eastern

  United States. 

C The migratory Canada geese do not interbreed with the nonmigratory Canada

  geese. 

D The migratory subspecies and the nonmigratory subspecies are not the only

  two subspecies of Canada geese. 

E The groups that have proposed allowing hunting of the nonmigratory geese

  have thoroughly studied both goose populations. 

答案B