There are places in the world where people are alleged （被认为) to live much longer and re

There are places in the world where people are alleged (被认为) to live much longer and remain more vigorous in old age than in most modern societies. I have visited the best known of these regions, all relatively remote and mountainous. A striking feature common to all three cultures is the high social status of the aged. Each of the very elderly persons I saw lived with family and close relatives—often an extensive household—and occupied a central and privileged position within this group. The sense of family continuity is strong. There is also a sense of usefulness. Even those well over 100 for the most part continue to perform. essential duties and contribute to the economy of the community. These duties included weeding in the fields, feeding the poultry (家禽), tending flocks, picking tea, washing the laundry, cleaning house, or caring for grandchildren, all on a regular daily basis. In addition, the aged are esteemed for the wisdom that is thought to derive from long experience, and their word in the family group is generally law. In none of the three communities is there any forced retirement age, and the elderly are not shelved, as occurs in most of our industrialized society. Khfaf Lasuria, the former tea picker, had retired only two years before I met her. When I asked Seliac Butba, age 121, if he was helping in the construction of a new house springing up next to his own, he responded, "Of course, they cant do without me. " Many of the centenarians emphasized the importance of being independent and free to do the things they enjoyed and wanted to do, and of maintaining a placid (平静的) state of mind free from worry or emotional strain. "Now everywhere people dont live so long because they dont live a free life," commented Sonia Kvedzenia of Atara, age 109. "They worry more and dont do what they want. " Gabriel Chapnian, 117, of Gulripshi expressed a similar thought when told that few Americans attain his age. His response: "Hmm...too literate. " Expectation of longevity may also be important. In America the traditional life-span is three score and ten years. But when we asked the young people of Abkhazia how long they expected to live, they generally said, "To a hundred". Dr Georgi Kaprashvili of Gulripshi confirmed that the public has the notion that the normal life-span of man is 100 years. For exaggeration, when proposing toasts, they say 300 years, but everyone expects to be 100.

What does the word "centenarian" (Line 1, Para. 6) mean in this passage？

A．Person who has 100 family members.

B．Person who is 100 or more years old.

C．Person who is the central figure.

D．Leader of a unit of 100 soldiers.

请帮忙给出正确答案和分析，谢谢！