If pqr = 1, the value of the expression $$1/(1+p+q^{-1}) + 1/(1+q+r^{-1}) + 1/(1+r+p^{-1})$$

A

p+q+r

B

1/(p+q+r)

C

1

D

$$p^{-1} + q^{-1} + r^{-1}$$