Prolonging human life has decreased the dependency load. In all societies ___1___ people are disable or too young or too old to work are dependent on the ___2___ rest of society to provide them. In hunting and gathering cultures old people ___3___ who could keep up might be left behind and die. In times of famine infants ___4___ might be allowed to die because they could not survive when their parents starved. whereas when their parents survived they could have another child. In most contemporary societies people feel it a obligation to keep people live whether or not they can work. There are a great many people who live ___5___ the past age in which they want to work or are able to work. there are rules ___6___ that require people to retire at a certain age. If these people are able to save ___7___ money from their retirement, somebody else must support them. In the Unite states many people live on social security checks, which are so considerable ___8___ that they must live in near poverty. Elder people are more liable to become ill than young or middle-aged people. ___9___ therefore they are wealthy or provided with private or government insurance, ___10___ they must often “go on welfare” if they fall seriously ill.
2. people后加who或that 分析句子结构，此句出现了两个谓语（系动词）are，故有一个必是从句。根据句子的主干可知，前部分are disable or too young or too old to work应该是定语从句，且缺少了引导词，又因为先行词是people，故加上相应的引导词that或who。
3. provide后加for 此处从句的意思是“没有工作能力的人由有工作能力的人来养活”。provide for sb是“养活某人”的意思。