When writing numbers in base 10 we only allow coefficients of 0 through 9 why is that?

What is hydroelectric power produced by?

During which phase does earth see more than half of the moon's surface? 1)first quarter2)third quarter3)waxing gibbous4)waning crescent

This comparative chart is an example of one that might be used by scientists and law enforcement personnel for identification purposes. the chart represents a technological advance called