$\int_{\alpha}^{\beta} \varphi(x) d x+\int_{\beta}^{\alpha} \varphi(x) d x=$ (a) 1 (b) $2 \int_{\alpha}^{\beta} \varphi(x) d x$ (c) $-2 \int_{\beta}^{\alpha} \varphi(x) d x$ (d) 0