单项选择题 引发事件冒泡时，要阻止事件冒泡可以使用（   ）语句 A.  preventDefault() B. stop( ) C. stopPropagation() D. return null

单项选择题 According to the author, which of the following is NOT a reason why science-fiction stories are believable? A、Many science-fiction authors are scientists. B、They are about situations that will one day be true. C、Old science-fiction stories include technology that has become a reality. D、They portray the true potential of humanity.

单项选择题 （        ）是技术美的基本条件，核心思想是用尽可能少的材料、能源、时间和人力的消耗来创造技术美 A. 审美 B. 经济原则 C. 操作 D. 效用