问题 选择题 若(1-i)(a-i)是纯虚数,则实数a=( )A.1B.-1C.2D.-2 答案 (1-i)(a-i)=a-1-(a+1)i.根据纯虚数的概念得出a-1=0,-(a+1)≠0,解得a=1故选A.