A) what two processes account for adding free oxygen to the precambrian atmosphere? b) what do we mean by free oxygen, and c) which of these two processes were most important?

Asap will mark geography final plz ! what are the benefits of international aid? (give me the right evidence )

Which of the following statements best describes what is occurring in the land surrounding the sahara desert? a desertification is increasing, and the desert is expanding. b. fewer people are trying to farm in this semiarid region. c. the desert is shrinking with the increased use of irrigation. d. increased urbanization has resulted in decreased deforestation. select the best answer from the choices provided mark this and return save and exit next submit

Which barrier to economic development is shown in the following examples?