Please, explain?

(df(y))/(dx) = d/(dy)(f(y)×(df(y))/(dx))

d...............d.............dy

--- (f(y)) = --- (f(y)) • ---............ANS (Option D)

dx.............dx...........dx

Yes D) is correct ; .....df / dx ≡ ( df / dw ) ( dw / dt ) (dt/dx) by the theorem on derivatives of Composite Functions...in algebra you remember that [ A B C } / [ B C H ] ≡ A / H...same holds for derivatives using ' symbols '

The Chain Rule: dz/dx = (dz/dy)•(dy/dx)

So, where f = f(y), df/dx = (df/dy)•(dy/dx)

d(f(y))/dx = (d(f(y))/dy)•(dy/dx)

Answer D