What is the total derivative of the function f(x,y) = ln(x+y), where ln() denotes the natural logarithmic function?

What is the total derivative of the function f(x,y) = ln(x+y), where ln() denotes the natural logarithmic function?
A . 1 / (x+y)
B . (x + y) / (x+y)
C . -x/(x+y) – y/(x+y)
D . ln(x+y) x + ln(x+y) y

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Answer: B