(Correction, B was not written clearly, if I guessed correctly it should be X1,2^2X2, ... ,n^2Xn , ...) Choice B, because a very important condition for satisfying the law of large numbers is that the variance has an upper bound, i.e., D(X)<=C, and after calculating this, we can see that the variance of the ACD option has a *** same upper bound of 1, whereas the variance in item B is n^2, so there is no upper bound, and it does not satisfy Chebyshev's law of large numbers.