单选题 Witnesses who ______ in a courtroom must swear to tell the troth when they speak for or against the person being tried.
【正确答案】 B
【答案解析】testify作证；modify(稍加)修改；satisfy使感到满意；qualify使合格。句意：当证人在法庭支持或反对正在受审的人而作证的时候，必须宣誓讲真话。