Why is $E(X_t|B_t)=\frac{E(X_tB_t)}{E(B_t^2)}B_t$?

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Why is $E(X_t|B_t)=\frac{E(X_tB_t)}{E(B_t^2)}B_t$ ? Does this always hold

In an exercise I have to show that $E(X_t|B_t)\neq X_t$, where $X_t=\int_0^t B_s ds$, I think the definition of $X_t$ does not play a big role here, or not ?