Let a curve \( y=f(x), f(x) \geq 0 \forall x \in R \) has property that for every point \( P \) on the curve, length of subnormal is equal to abscissa of \( P \). If \( f(1)=3 \), then \( f(4) \) is equal to
(A) \( -2 \sqrt{6} \)
(B) \( 2 \sqrt{6} \)
(C) \( 3 \sqrt{5} \)
(D) none of these