Differentiation

Let y = f(x) be a differential function for all x Îµ R . Then which of the following is always true :

(a) d²ydx² - (dxdy)³ =0
(b) d²ydx² + (dxdy)³ . d²xdy² =0
(c) d²ydx² - (dydx)³ =0
(d) none of these

Can u plz help me in this.....

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