Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the question.

The world needs to do more to prepare for the impact of a rapidly aging population, the UN has warned - particularly in developing countries. Within 10 years the number of people aged over 60 will pass one billion, a report by the UN Population Fund said. The demographic shift will present huge challenges to countries' welfare, pension and healthcare systems. The UN agency also said more had to be done to tackle "abuse, neglect and violence against older persons".

The number of older people worldwide is growing faster than any other age group. The report, Ageing in the 21st Century: A Celebration and a Challenge, estimates that one in nine people around the world is older than 60. The elderly population is expected to swell by 200 million in the next decade to surpass one billion, and reach two billion by 2050. This rising proportion of older people is a consequence of success - improved nutrition, sanitation, healthcare, education and economic well-being are contributing factors, the report says.

But the UN and a charity that also contributed to the report, Help Age International, say the aging population is being widely mismanaged. "In many developing countries with large populations of young people, the challenge is that governments have not put policies and practices in place to support their current older populations or made enough preparations for 2050," the agencies said in a joint statement.

The number of the elderly rises because of the following reasons, EXCEPT ________.