What causes photochemical smog?
a. it is formed by reactions involving sunlight and nitrous oxides and hydrocarbons released from automobile exhaust.
b. it is formed from sulfur oxides and particulate matter released from combustion of combustion of heating oil and coal.
c. it is formed by reactions between cfcs from industrial processes and ice crystals in the upper atmosphere.
d. it is formed when secondary pollutants such as ozone combine with primary pollutants such as hydrocarbons in cold winter temperatures?

Even though the ostrich is a flightless bird, ostriches still possess wings that stretch approximately two meters across when fully extended. scientists speculate that when dinosaurs became extinct, some of the birds that lived during that time became land dwellers since they were able to consume the food that the dinosaurs once ate. over time, these species grew larger and heavier. eventually, the ostrich species became too big to fly. the wings found on ostriches are known as a. analogous structures. b. homologous structures. c. vestigial structures. d. symmetrical structures.