GWD14的一道逻辑题！！求解释。。

11. GWD17-Q11:

Some species of Arctic birds are threatened by recent sharp increases in the population of snow geese, which breed in the Arctic and are displacing birds of less vigorous species.Although snow geese are a popular quarry for hunters in the southern regions where they winter, the hunting season ends if and when hunting has reduced the population by five percent, according to official estimates.Clearly, dropping this restriction would allow the other species to recover.

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

A.Hunting limits for snow geese were imposed many years ago in response to a sharp decline in the population of snow geese.

B.It has been many years since the restriction led to the hunting season for snow geese being closed earlier than the scheduled date.

C.The number of snow geese taken by hunters each year has grown every year for several years.

D.As their population has increased, snow geese have recolonized wintering grounds that they had not used for several seasons.

E.In the snow goose’s winter habitats, the goose faces no significant natural predation.

答案是B。
题目读不懂（下划线部分），麻烦大家解释一下吧！！
有一点我很奇怪，题中突然蹦出来个restriction。。。之前没说有什么限制啊？？