A．(A) Because they are the source of admiration from their peers.

B．(B) Because they can prepare children for the complexity in later life.

C．(C) Because they cost the parents less than the desserts and toys.

D．(D) Because they can help the children become more consistent in future.

在南海某岛上迁入一些农户，那里土地肥沃，气候宜人，若干年后，岛上人口增长如右图曲线所示，请回答：

当人口数量强行增长到O点时，就会很快下降至P点，原因是人口剧增后，岛上生活资源发生短缺，人们为争夺生活资源加剧了（），各种因素破坏了该岛生态系统的（），导致部分人口迁出。