5. 已知直线l:(a−2)x+y−3=0l:(a-2)x+y-3=0l:(a−2)x+y−3=0,圆C:(x−1)2+y2=5C:(x-1)^{2}+y^{2}=5C:(x−1)2+y2=5.则"a=0a=0a=0"是"lll与CCC相切"的((( )))