This is just about feasible at the moment, when centenarians are still comparatively rare, but it will not be the case for much longer.

The past few weeks, however, have been one of those rare phases.

Though for most organisms the sudden appearance of new resistance is rare, this is not the case for all pathogens.

Purple is a very rare color in nature; some people consider it to be artificial.

The extraterrestrials may be out there, and we might learn much by discovering them, but it is paranoia of a rare sort that would shutter the Earth out of fear that they might discover us.