【题目】It was how the young man had learned five foreign languages attracted the audience's interest.
在线课程【答案】that
【解析】分析句子结构可以看到，how the young man had learned five foreign languages是一个意义完整的句子，可以理解为attracted的主语。去掉It was和空格处，句意完整，that只起连接作用，在句中不作任何成分，所以此句是强调句式。所以答案是that。