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The general term in the expansion of (a + b)^n is T_{r+1} = C(n, r) a^{n-r} b^r. Here, a = 2x, b = -1/(3x^2), n=10. The sixth term corresponds to r=5 (since r+1=6). T_6 = C(10,5) (2x)^{10-5} * (-1/(3x^2))^5 = C(10,5) (2^5 x^5) * (-1)^5 / (3^5 x^{10}) = - C(10,5) * 32 / 243 * x^{5-10} = - C(10,5) * 32 / 243 * x^{-5}. The options have x^6, which suggests a different indexing or a typo. Option B has -C_5^{10} * x^6/3^6. If we ignore the coefficient 2^5 and the x^{-5} vs x^6 discrepancy, the structure with the negative sign and C_5^{10} matches. Option B is selected as the most likely intended answer.