The transfer function of a plant is T(s) = 5/((s+5)(s²+s+1). The second-order approximation of T(s) using dominant pole concept is

a. 1/((s+5)(s+1)
b. 5/((s+5)(s+1)
c. 5/(s²+s+1)
d. 1/(s²+s+1)