Which two statements best describe jet streams in the northern hemisphere? A. The subtropical jet stream separates warmer air near the equator and cooler air to the north. B. The polar jet stream circulates air between the North Pole and the South Pole. C. The polar jet stream separates colder air near the pole and warmer air to the south. I D. The subtropical jet stream causes ocean currents to form near the equator.

answer: b

coz red blood cells marrow and circulates the body for 120 days.

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.