For laminar flow (NRe < 2100) in steel pipe, the optimum inside pipe diameter is given by____________________?

A. Di, opt = 3 Q0.36 ρ0.18
B. Di, opt = 3.9 Q0.45 ρ0.23
C. Di, opt = 7.6 Q0.36 ρ0.9
D. Di, opt = 3 Q0.36 ρ1.86 μ0.08