Which of the following is an example of a trade surplus? a.) Country D exports $100 billion worth of goods and imports $200 billion worth of goods. b.) Country B exports $300 billion worth of goods and imports $400 billion worth of goods. c.) Country A exports $200 billion worth of goods and imports $150 billion worth of goods. d.) Country C exports $500 billion worth of goods and imports $500 billion worth of goods