碳的相对原子质量是（　　）

A．12g

B．12

C．1/12

D．1.66×10^-27kg

Which of the following is true regarding estimation ？（）

A．PERT is superior to CPM

B．PERT estimates are better than Monte Carlo simulation

C．CPM uses 3 estimates on a task(pessimistic, optimistic and most likely)

D．Monte Carlo simulation uses PERT formula