下列由极性键构成的非极性分子是（       ）

A．N₂

B．HF

C．NH₃

D．CO₂

You are trying to determine what cost and schedule trade-off will be most appropriate for your project. You have the option to select either a more experienced person at $120 per hour who can do the task in 45 days or a less experienced person at $80 per hour who can do the same task in 65 days. A tool you can use to facilitate making the decision is （）.

A．cost of quality

B．cause-and-effect diagram

C．design of experiments

D．network diagrams