【单选题】The fact that a rock star earns $5 million a year while a teacher earns $25,000 annually is most directly an example of an economy answering the ( ) part of one of the two big economic questions.
【简答题】(一) . 语法填空 1 . Mary is interested in biology and wants to be a ______ (biology) when she grows up. 2 . As a result of this , a great dust cloud formed in the sky __________ _______ ( 阻挡 ) the sun...