4.【答案】A【解桥:音>1y-((分)广为增函数b-(号)广'<(子)广-e又:<34<3时∴lg4<专即a
a1十3d=2,故S=7a,十21d=7(a1十3d)=14.
6.【答案】A【解折1-5,且号三红-一2-6一空红-2-3初.故所求6个数的方差为行[之红-2+6-5门]=5