Making a connection: variable stars change their brightness periodically. which of our daily life devices, instruments etc. change their brightness or/and size alike variables. give examples, explain differences and similarities. (astronomy)

How did the europeans design the national borders of africa? why?

17. the soil erosion pictured here is the result of what? a. harvesting renewable resources at a rate greater than the sustainable yield b. a mudslide caused by excessive rains c. harvesting renewable resources at a rate lower than the sustainable yield d. the transition between geologic eras and eons

Which city area has the most accessible oil reserves a) caspian sea b) siberia c)arctic coast d)lake baikal