Two resistors with nominal resistance values R1 and R2 have additive uncertainties ΔR1 and ΔR2, respectively. When these resistances are connected in parallel, the standard deviation of the error in the equivalent resistance R is

• A. \(\pm \sqrt {{{\left( {\frac{{\partial R}}{{\partial {R_1}}}{\rm{\Delta }}{R_1}} \right)}^2} + {{\left( {\frac{{\partial R}}{{\partial {R_2}}}{\rm{\Delta }}{R_2}} \right)}^2}} \)
• B. \(\pm \sqrt {{{\left( {\frac{{\partial R}}{{\partial {R_2}}}{\rm{\Delta }}{R_1}} \right)}^2} + {{\left( {\frac{{\partial R}}{{\partial {R_1}}}{\rm{\Delta }}{R_2}} \right)}^2}} \)
• C. \(\pm \sqrt {{{\left( {\frac{{\partial R}}{{\partial {R_1}}}} \right)}^2}{\rm{\Delta }}{R_2} + {{\left( {\frac{{\partial R}}{{\partial {R_2}}}} \right)}^2}{\rm{\Delta }}{R_1}} \)
• D. \(\pm \sqrt {{{\left( {\frac{{\partial R}}{{\partial {R_1}}}} \right)}^2}{\rm{\Delta }}{R_1} + {{\left( {\frac{{\partial R}}{{\partial {R_2}}}} \right)}^2}{\rm{\Delta }}{R_2}} \)