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In the figure is $\mathrm{A}^{1} \mathrm{~A}^{2}$ and $\mathrm{A}^{3}$ are ideal ammeters. If $\mathrm{A}^{1}$ reads $5 \mathrm{~A}, \mathrm{~A}^{2}$ reads $12 \mathrm{~A}$, then $\mathrm{A}^{3}$ should read.

1. $7 \mathrm{~A}$
2. $12 \mathrm{~A}$
3. $13 \mathrm{~A}$
4. $17 \mathrm{~A}$