单选题 The international marketing conferences, such as those held in association with regional business meetings, are ______ sources for business opportunities.
【正确答案】 B
【答案解析】[解析] 单词形态：形容词
1．这是一道单词形态选择题，选项均为excel的不同形式。
2．空格内应填入一个修饰名词的形容词，因此B．excellent为正确选项。