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If $q^{-a} = \frac{1}{r}$ and $r^{-b}=\frac{1}{s}$ and $s^{-c} = \frac{1}{q}$ ,the value of $abc$ is______.

1. $(rqs)^{-1}$
2. $0$
3. $1$
4. $r+q+s$