This stamp is probably highly valuable, since it exhibits a printing error. The most important factors in determining a stamp's value, assuming it is in good condition, are its rarity and age. This is clearly a fine specimen, and it is quite old as well.

Question: The conclusion is properly inferred if which one of the following is assumed?
Options:
A. The older a stamp is, the more valuable it is.
B. Printing errors are always confined to a few individual stamps.
C. Most stamps with printing errors are already in the hands of collectors.
D. Rarity and age are of equal importance to a stamp's value.
E. Even old and rare stamps are usually not valuable if they are in poor condition.
Answer: "B"