For sum z>2,the integration interval 1<x<z−1 has length z−2,giving A. Its survival at 4 is ∫₄∞4(z−2)/z³ dz=3/4. Its mean integral has tail proportional to ∫dz/z and diverges,so C is false. The marginal f_X(x)=2/(x+1)² and conditional integration give E(Y|X=x)=x+2,hence D. **C**.
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