Which of the following is a difference between arteries and viens? arteries carry blood and veins carry only plasma
arteries do not have valves and veins do have valves
arteries are thin and veins are thick
arteries carry blood back to the heart and veins carry blood to the heart

Which of the following factors would not contribute to allopatric speciation? a) a population becomes geographically isolated from the parent population. b) the separated population is small, and genetic drift occurs. c) the isolated population is exposed to different selection pressures than the ancestral population. d) different mutations begin to distinguish the gene pools of the separated populations. e) gene flow between the two populations is extensive.