单选题   You should extend your hand when you hold it out to shake hands with someone. The underlined part means ______.
 
【正确答案】 C
【答案解析】句意：当和别人握手的时候你要伸出手臂。extend伸出(手臂等)。prolong延长，拖延。lengthen使变长，延长。stretch伸展，伸长。