Of all the threats to human society, including war, disease and natural disaster, one outranks all others. It is the aging of the human population. The __________ of people aged 60-plus around the world is ________to more than double in 2050. By 2047, for the first time in human history, the number of old people is projected to exceed that of children on the planet. This change will have ________ impacts on human society. One problem concerns the ratio of the number of people of working age to the number of older people, which is known as the " ___________support ratio". This index has fallen from 12 in 1950 to 8 in 2013 and is expected to drop to 4 in 2050. Its decline means that the burden on the young, __________and socially, will rise accordingly. This is because older people rely on the young, not only for care and support but also for the economic productivity that _________ pensions can be paid and health and social costs met. A variety of issues in other areas such as family composition, the transfer of property, taxation and housing may _________ from the population "age-quake", too. For instance, family ties have been weakened by increased mobility and rising divorce, and hence the demand for _____________ and nursing homes will increase since more older people will need to live in an institution or elder care center. No matter what the future reality will be, the aging of the human population certainly ________ a challenge to policy makers, economists and health care specialists around the world. This suggests that the human society will need to be _________ into a structure that has the ability and resources to address the diverse needs of older people.