Many copies, due to numerous reprints its partically difficult to calculate

Generally speaking, travel in Greece is difficult because of the numerous mountain ranges and expense of sea-travel.

It is difficult to interpret recent history and current events because there are numerous and variable interpretations of events and their significance. Historical research is not an exact science, so it may not be possible to uncover what actually happened. It is also difficult to see a recent or current event from an historical perspective.

airscraft cariers are ard to sink they would take numerous shots about 3 buy a torpedo by machine gun about 50 -jggammer

A density dependent inhibition is when cells become more and more numerous, the required growth factors and nutrients become insufficient making cell growth difficult.