PT 63 S3 Q21

Chemist: The molecules of a certain weed-killer arealways present in two ... ...

Which one of the following, if true, most strengthens the chemist’s argument?
(A) In general, if the molecules of a weed-killer are always present in two forms, then it is likely that weeds are killed by one of those two forms but unaffected by the other.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in June 2011 LSAT (PT 63): Logical Reasoning B