Assume you were Jack, Director of International Investment. Briefly explain the ranking principle for capital allocation when the capital is limited, and calculate the present value index for Project A, Project B, and Project C. With a total investment of l billion Hong Kong dollars (HKD 1 000 000 000) , determine the available combinations of project investment options. Lastly, suggest to the management the best investment decision and provide a reason to support your decision.

我国宋代的学术著作《梦溪笔谈》中有如下一段叙述：“方家（指精通某种学问的行家）以磁石磨针锋，则能指南，然常微偏东，不全南也（不是正南方向）。”以上叙述的现象证明地球是一个____________，并且以事实说明了地理的两极与地磁的两极_________________。