∵{an}是等差数列 a2，a4，a7成等比数列，∴a42=a2a7即（a1+3d）2=（a1+d）（a1+6d）整理得：a1d-3d2=0∵d≠0∴a1=3d∴ S10 S5 = 10(2a1+9d) 2 5(2a1+4d) 2 = 2a1+9d a1+2d = 15d 5d =3故选：C
