7.C【解析】由s=0,k=0满足条件,则k=2,s=,满足条件;k=4,s=+=3,满足条件;k=6s=31111254+612,满足条件;8,12+8-24,不满足条件输出k8,所以应填“12”,故选C1218.A【解析】因为3x∈,2,使得2-x+1<0成立是假命题,所以x∈22x2-x+1≥0恒成立是真命题,即x∈[,2,≤2x+恒成立是真命题,令(x)=2x+,则f(x)=2-当x∈[),(x<,当x∈(2时,(x)>0,所以f(x)≥()=22,则22选A