The young speaker smiled to the audience _____ as he walked into

The young speaker smiled to the audience _____ as he walked into the lecture hall. (humble)
【正确答案】：humbly
【题目解析】：译文：年轻的演讲家走进演讲大厅的时候，向观众谦逊地笑了一下。humble修饰动词smile,应用其副词形式。答案为humbly。