Three Resistors with Values R₁, R₂, and R₃, Respectively, Are

Three resistors with values R₁, R₂, and R₃, respectively, are connected in parallel. Which of the following expresses the total resistance, R_T, of the three resistors when connected in parallel?

A) R_T = (1/R₁ + 1/R₂ + 1/R₃)
B) R_T = R₁ = R₂ = R₃
C) R_T = R₁ + R₂ + R₃
D) R_T = (1/R₁ + 1/R₂ + 1/R₃) ^{- 1}