Do you want to live another 100 years or more? Some experts say that scientific progress will one day help humans to last tens of years longer than what is now seen as the natural limit（限制）of the human life span（寿命）.
“ I think we are knocking at the door of immortality (永生),” said Michael Zey, a Montclair State University business professor and author of two books on the future. “ I think by 2075 we will see it and that’s a conservative estimate（保守估计）.”
At the conference in San Francisco, Donald Louria, a professor at New Jersey Medical School in Newark said progress in using genes as well as nanotechnology（纳米技术）makes it likely that humans will live in the future beyond what has been possible in the past. “ There is a great push so that people can live from 120 to 180 years,” he said. “ Some have suggested that there is no limit and that people could live to 200 or 300 or 500 years.”
However, many scientists who research into aging are doubtful about it and say the human body is just not designed to last about 120 years. Even with healthier lifestyles and less disease, they say failure of the brain and organs will finally lead all humans to death.
Scientists also disagree on what kind of life the super aged might live. “It remains to be seen whether you could be healthy enough to have good quality of life when you pass 120.” said Leonard Poon, director of the University of Georgia Gerontology Center. “ At present people who could get to that point are not in good health at all.”
By saying “ we are knocking at the door immortality”, Michael Zey means_____.

A．they believe that there is no limit of living

B．they are sure to find the truth about long living

C．they have got some ideas about long living

D．they are able to make people live beyond the present life span

Donald Louria’s attitude toward long living is that_____.

A．people can live from 120 to 180

B．it is still doubtful how long humans can live

C．the human body is designed to last about 120 years

D．it is possible for humans to live longer in the future

The underlined “ it” (Para. 4) refers to_____.  

A．a great push

B．the idea of living beyond the present life span

C．the idea of living from 200 to 300

D．the conservative estimate

What would be the best title for this text?

A．Living longer or not

B．Science, technology and long living

C．No limit for human life

D．Healthy lifestyle and long living