Which sources do scientists use to study ancient climates? check all that apply. earth’s orbit tree rings volcanoes pollen grains fossils

Using complete sentences, describe the central economic problem facing all humans. why does this require people to make choices? how can this result in opportunity costs?

Why does less erosion & more deposition take place on the outside bank of a meander?

Residents of moldova are mainly a. russian b. ukrainian c. serbian d. romanian the answer is d. romanian