Americans sometimes feel that treating a guest as one of the family will make him feel more comfortable. Sometimes American families have "buffet" style dinners because they are informal and easier to serve, especially if there are several guests.

A. 为了达到2000年的6.4亿人口的估计，当前每年的2%的增长率必须是基础．
B. 据估计，以当前每年2%的增长率来推论到2000年时人口是6.4亿。
C. 2000年，6.4亿人口的估计是基于现阶段每年2%的增长率基础之上的。
D. 到2000年时人口将达到64亿，这是根据目前2%的年增长率所做出的估计。