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first and second axes are for M 2 and s$_{0}$ , and third axis is for the ratio of the continuum contribution over the total contribution for criteria (A) and the ratio of the dimension-six contribution over the total contribution for criteria (B) respectively. By setting a fixed value for s$_{0}$ , it is found that the continue contribution increases with the increment of M 2 and the contribution from the dimension-six condensate term increases with the decrement of M $^{2}$, so criterion (A) determines the upper limit of M 2 and criterion (B) determines the lower limit of M $^{2}$. Then, a possible Borel window can be obtained from criteria (A) and (B), which shall be further constrained by criterion (C). Practically, the range of ( M $^{2}$,s$_{0}$ ) can be determined numerically. The left diagram of Fig.(3) shows the allowable range of ( M $^{2}$,s$_{0}$ ) for sum rules I, which is obtained by sampling 500 × 400 points within M 2 ∈ [2 , 7] GeV 2 and s$_{0}$ ∈ [32 , 36] GeV $^{2}$. And the left diagram of Fig.(4) shows the allowable range of ( M $^{2}$,s$_{0}$ ) for 

