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Consider points $\mathrm{P}$ and $\mathrm{Q}$ in the $x-y$ plane, with $P=(1,0)$ and $Q=(0,1)$. The line integral $2 \int_{P}^{Q}(x d x+y d y)$ along the semicircle with the line segment $P Q$ as its diameter

1. is $-1$
2. is $0$
3. is $1$
4. depends on the direction (clockwise or anti-clockwise) of the semicircle