as we observed by using different combinations of various SNIa and BAO data sets disappear when we use the Wetterich parametrization to replace the CPL parametrization. This again brings the problem as raised in [11] that the CPL parametrization might be blamed to be not so versatile. In order to disclose the exact answer, we have to examine more models of DE. This work offers the attempt of using different combinations of various data sets at low and high redshifts to examine the effects of data systematics on the evolution of the DE and the acceleration of the universe. Further investigation along this line by including more data sets and examining more DE models are called for and we will report our progress in this direction in the future work. RGC and BW thank Chongqing University of Posts and Telecommunications for the warm hospitality during their visits. This work was partially supported by NNSF of China (Nos. 10821504, 10878001, 10975168 and 10935013) and the National Basic Research Program of China under grant No. 2010CB833004. YG was partially supported by the Natural Science Foundation Project of CQ CSTC under grant No. 2009BA4050. Acknowledgments 14 [1] A.G. Riess et al. , Astron. J. 116 , 1009 (1998). [2] S. Perlmutter et al. , Astrophy. J. 517 , 565 (1999). [3] Y.G. Gong and A. Wang, Phys. Rev. D 75 , 043520 (2007). [4] Y.G. Gong, R.G. Cai, Y, Chen and Z.H. Zhu, arXiv: 0909.0596, J. Cosmol. Astropart. Phys. in press. [5] V. Sahni, A. Shafieloo and A.A. Starobinsky, Phys. Rev. D 78 , 103502 (2008). [6] M. Hicken et al. , Astrophys. J. 700 , 1097 (2009). [7] W.J. Percival et al. , Mont. Not. R. Astron. Soc. 381 , 1053 (2007). [8] W.J. Percival et al. , arXiv: 0907.1660. [9] M. Chevallier and D. Polarski, Int. J. Mod. Phys. 10 , 213 (2001). [10] E.V. Linder, Phys. Rev. Lett. 90 , 091301 (2003). [11] A. Shafieloo, V. Sahni and A.A. Starobinsky, Phys. Rev. D 80 , 101301 (2009).