8.设iii是虚数单位,已知复数zzz满足(1−i)z=1+(a−1)i(a∈R)(1-i)z=1+(a-1)i(a\in R)(1−i)z=1+(a−1)i(a∈R),且复数zzz是纯虚数,则实数a=(a=(a=( )))