Which of the following scenarios represents change to an ecosystem brought about by biotic factors?

a. a wildfire caused by lightning striking a tree
b. a flood caused by a severe storm

c. a landslide caused by cattle overgrazing

d. a volcano

The world wars of the twentieth century immediately led to a. the establishment of a communist bloc in eastern europe b. the urbanization of europe’s societies c. an emphasis on humanism d. an emphasis on ties to greek and roman societies select the best answer from the choices provided. a b c d