In a (n) system, two stars orbit each other

What is the rule relating the ratio of marginal utility to prices of two goods at the optimal choice? explain why, if this rule does not hold, the choice cannot be utility-maximizing.

How is germany's location in europe an advantage during wwii?

The persian wars started when emperor darius i began an invasion of greece. what caused darius to decide to attack greece? a. greek pirates had raided persia's merchant ships and coastal towns. b. greek armies had attacked and taken over land that belonged to persia. c. greek city-states had supported rebellions in the persian empire. d. greek leaders had declared independence from the persian empire.