问题补充：
单选题Canadahasvastareasofwilderness,fromtheArcticnorth,_______averagewintertemperaturesareusually-200C,totheborderwiththeUSAinthesouth,_______issaidtobethelongestborderintheworldnotdefended.A.which, whereB.whose, whichC.where, whereD.where, which
答案：
D
