Who were the Proto-Indo-European people, and how did their significant innovation foster the development of European civilization ?

Shari is trying to decide how she should use her cash birthday gifts. her choices are new clothes, a concert ticket, or donating the money to her favorite charity. shari decides to donate the money. the value given up by not choosing both the clothes and the concert ticket is called a . a.) trade-off b.) opportunity cost c.) retail price