签证上没此条件，大多数人也必须申请豁免

只要你的专业在此List上，对大多数国家的人，就需申请豁免。
Exchange Visitor Skills List
http://exchanges.state.gov/education/jexchanges/participation/waivers.htm

An advisory opinion is a request for a statement from the Waiver Review Division as to whether an exchange visitor is subject to Section 212(e) of the Immigration and Nationality Act, as amended.