加动名词I'm surprised at seeing you.
加 动名词啊~~ AT是介词~
be surprised at sth./sb.对某人或某人感到惊讶I am surprised at his act. 我对他的行为感到惊奇
at是介词，后面跟名词或者动名词，或者是从句
动名词介宾短语I am surprised at his being ill
