The 1918 influenza epidemic killed between 50 million and 100 million people worldwide. this epidemic happened near the end of world war i. more people died from the influenza epidemic than were killed in the war. which of the following explains why this virus was so deadly worldwide?
a) infected soldiers returning from the war spread the virus when they coughed.
b) food was scarce because of the war, so people were undernourished, and their immune systems were weakened.
c) medical personnel often became ill as a result of exposure to airborne virus particles.
d) all of the above

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.