S196.已知等差数列{an}的前n项和为52a,,公比为的等比数列,则q等于1(BA.1或2B.1或3C2D.33a1(【解析】∵a1,,a5成公比为q的等比数列,数列{an}为等差数列,:a14gc33∴(a1+d)2=a1(a1+4d),∴d=0或d=2a1,∴q=1q=3,故选B(x+y≥0,7.若x,y满足{x≥1,则下列不等式恒成立的是(D)x-y≥0Ax≥2Bx-2y≥0Cx+2y≥0D.2x-y-1≥0【解析】选项A显然错误令z=2x-y,画出可行城,由图知,当x=y=1时,=1,故选项D正确,同理可验证选项B、C错误