已知直线l:y=kx+b,曲线C:x2+y2=1,则“b=1”是“直线l与曲线C有公共点”的( )
Mr. Liu is a ____. He works in Bao'an People's Hospital. His house is ____ from the hospital. So he goes to work by ____.He is ____. He helps lots of sick people. He likes his ____.