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1) The existence of complex molecular structures present in every living system is used by Drexler to show the theoretical possibility of the design and construction of equally or more complex structures with means of molecular engineering.
2) He describe his vision of a world where molecular manufacturing would allow people to manufacture anything they might need simply by feeding waste material into a box that would use nanoscale assemblers to re-configure it into the necessary form.
3) Rather that its utopian promise, Drexler’s book is remembered for the warning that as this technology developed it would be necessary to guard against the accidental release of autonomous self-replicating nano-machines that could turn the planet into a mass of uninhabitable ‘grey goo’.
4) The grey-goo scenario is based on the fear that the self-replicating nanotechnological devices may destroy the natural world.
5) With his theory, Drexler has played an important role in generating both excitement and fear about nanotechnology over the years.
6) But, although his reflections are technically based, today there aren’t convincing experimental or engineering demonstrations to support his future scenery, so many scientist consider to be scientifically and socially infeasible the idea of nanotechnology as molecular manufacturing.

1) ok

2) He described ...
3) Rather than its.....
4) May, or could?
5) With his vision, Drexler has....
6) But today, there are no current convincing demonstrations to support .... scientists consider infeasible the idea of molecular manufacturing with nanotechnology.