题目

-Can you describe____？-Yes． I was walking when a bike knocked me down from behind．A. why did the accident happenB. when did the accident happenC. how the accident happenedD. where the accident happened 答案：【答案】C【解析】句意：-你能描述一下事故是怎样发生的吗？-好的，我正在散步这时一辆自行车从后面把我撞倒了。why did the accident happen为什么发生事故；when did the accident happen事故什么时候发生；how the accident happen事故是怎样发生的；where the accident happened事故发生在哪里。根据句子结构可知，这里考人人生来就有，不针对某一特定的病原体，而是对多种病原体都有防御作用，这种免疫叫做（ ）A．后天性免疫B．计划免疫C．特异性免疫D．非特异性免疫