【简答题】It is believed that it took about 800 thousand to 1 million years for the earth's population to reach the 250 million total which existed at the end of the first century AD. For some time after that, ...
【单选题】The population of the United States is only 6% the world's population, but Americans (1)_____ one third of all the energy (2)_____ in the world. This fact alone says that Americans need to use less en...