Question: partial differentiation

I was wondering if maple can compute partial derivatives. Suppose i have the the function z=a*f(x)+b*g(y)+c*x+d*y, can i obtain the partial derivative dz/df(x)=a, or the PARTIAL derivative dz/dx=c. diff(z,x); only seems to give the total derivative: dz/dx=df(x)/dx+c; Hope anyone can help, thanx Rick
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