scattering surface. In addition to employing the CMB shift parameter R by defining the reduced distance in the flat universe to the last scattering surface z$_{∗}$ as done in [11] we will add the acoustic scale l$_{a}$ in the data analysis. The acoustic scale l$_{a}$ is defined by where the redshift z$_{∗}$ is given by [21] We have three fitting parameters x$_{i}$ = ( R, l$_{a}$, z$_{∗}$ ) to include the CMB information now. Thus we have χ 2 $_{cmb}$( p , h, Ω$_{b}$ h $^{2}$) = ∑ ij Δ x$_{i}$ Cov − $^{1}$( x$_{i}$, x$_{j}$ )Δ x$_{j}$ , Δ x$_{i}$ = x$_{i}$ − x obs i and Cov( x$_{i}$, x$_{j}$ ) is the covariance matrix for the three parameters [22]. The CMB information provides a systematic check of the DE model by combining with the low redshift SNIa and BAO data sets. We employ the Monte-Carlo Markov Chain (MCMC) method to explore the parameter space p and the nuisance parameters h and Ω$_{b}$ h 2 in the data analysis. Our MCMC code [18] is based on the publicly available package COSMOMC [23]. We first explore the widely used CPL parametrization [9, 10] In this model, the dimensionless Hubble parameter for a flat universe is In this model, we have three parameters p = (Ω$_{m}$$_{0}$ , w$_{0}$, w$_{a}$ ). Knowing the expansion history of the universe, we can construct the Om diagnostic by defining 6 Om ( z ) = E $^{2}$( z ) − 1 (1 + z ) 3 − 1 . (17) E $^{2}$( z ) = H $^{2}$( z ) H 2 0 = Ω$_{m}$$_{0}$(1 + z ) 3 + (1 − Ω$_{m}$$_{0}$)(1 + z ) 3(1+ w 0 + w a $^{)}$exp( − 3 w$_{a}$z/ (1 + z )) . (16) w ( z ) = w$_{0}$ + w$_{a}$ z 1 + z . (15) g$_{1}$ = 0 . 0783(Ω$_{b}$ h $^{2}$) − 0 . 238 1 + 39 . 5(Ω$_{b}$ h $^{2}$)0 . $_{763}$, g$_{2}$ = 0 . 560 1 + 21 . 1(Ω$_{b}$ h $^{2}$)1 . $_{81}$. (14) z$_{∗}$ = 1048[1 + 0 . 00124(Ω$_{b}$ h $^{2}$) − 0 . $^{738}$][1 + g$_{1}$ (Ω$_{m}$$_{0}$ h $^{2}$) g 2 ] = 1090 . 04 ± 0 . 93 , (13) l$_{a}$ = πd$_{L}$ ( z$_{∗}$ ) (1 + z$_{∗}$ ) r$_{s}$ ( z$_{∗}$ ) = 302 . 1 ± 0 . 86 , (12) R ( p ) = √ Ω$_{m}$$_{0}$ ∫ z$_{∗}$ 0 dz E ( z ) = 1 . 71 ± 0 . 019 , (11) III. FITTING RESULTS