Modern industrial society grants little status to old people. In fact, such a society has a system of built-in obsolescence. There is no formal system for continuing our education throughout our life in order to keep up with rapidly changing knowledge. When our education and job skills have grown obsolete, we are treated exactly like those who have never gained an education or job skills and are not encouraged or given the opportunity to begin anew.
As a society becomes more highly developed, the overall status of older people diminishes. Improved health technology creates a large pool of old people, who compete for jobs with the young. However, economic technology lowers the demand for workers and creates new jobs for which the skills of the aged are obsolete, forcing older people into retirement. At the same time, young people are being educated in the new technology and are keeping pace with rapid changes in knowledge. Finally, urbanization creates age-segregated neighborhoods. Because the old live on fixed incomes, they must often live in inferior housing. All these factors—retirement, obsolete knowledge and skills, inferior standards of living—lower the status of the aged in society.
A century ago, when one could expect to live only to 50 or so, the life span more or less coincided with the occupation and family cycle. But today the average life span allows for fifteen to twenty years of life after these cycles. It appears that our life span is outpacing our usefulness in society.

The sentence "our life span outpaces our usefulness" means we can live longer ______.

A．and make progress

B．and do more work

C．but move slowly

D．but become useless

强直性脊柱炎的影像学表现不对的是（）

A.本病往往自骶髂关节开始，双侧发病常见

B.骶髂关节改变从骶髂关节的下2/3处开始，早期关节边缘模糊，主要发生在关节的髂骨侧，骶骨侧改变轻微

C.病变晚期，骶髂关节发生骨性强直

D.椎体变方，病变晚期脊椎呈竹节状强直

E.髋关节是强直性脊柱炎最常侵犯的外周关节，多为单侧受累