The best and most correct answer among the choices provided by the question is the second choice. The cause of studying rocket technology was that to explore the "last frontier". I hope my answer has come to your help. God bless and have a nice day ahead!
<span>Barter is a system of exchange where goods or services are directly exchanged for other goods or services without using a medium of exchange, such as money. It is distinguishable from gift economies in many ways; one of them is that the reciprocal exchange is immediate and not delayed in time.</span>
He inherited the principality of Moscow
