Is the Xor of the PRG, out put the PRG

I have question in learning PRG, by given f and f1 are prg. Both of them are {0,1}^n -> {0,1}^2n. Is g(X) = f(x) xor f1(x) a PRG. Someone told me that at this case, g(x) is not a PRG, but I don’t know how to prove it.

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