11.   And the scientists knew from experience in patients that bacteria exposed to penicillin could switch on an enzyme that destroyed the drug.

12.   As far as scientists know, that is a clear impossibility.

13.   As every political scientist knows, an economy humming along is the single greatest asset than any presidential can ever own.

14.   As far as scientists know, other, smaller planets may orbit these stars.

15.   Asked how scientists can know what to say and what to hold back, Hecker said that security experts at the lab provide frequent briefings on all security policies.

16.   Asteroids and comets are very different, and scientists know less than they would like to know about either.

17.   At the moment, as I say, scientists know of no possible origin.

18.   At the same time, scientists know that the bulk of their work in deciphering that sequence has yet to be done.

19.   Besides being infectious, the AIDS virus has been extensively studied, so that scientists know how to modify it.

20.   All the scientists know is that radio waves behave differently going in different directions.