题目

x,y,z∈R+,x+y+z=1,下列各式正确的是……( )A.x2+y2+z2≥1B.x2+y2+z2≥2C.xy+yz+xz≥D.x2+y2+z2≥ 答案：解析:由于x2+y2+z2≥xy+yz+xz,又1=(x+y+z)2=x2+y2+z2+2(xy+yz+xz),∴3(x2+y2+z2)≥1.则x2+y2+z2≥.故选D.答案:DI don’t know if she ___________. If she ___________tomorrow, I will tell you .A.will come; comes B.comes; comesC.comes; will come D.will come; came