题目

He came running along and climbed ____ the train just as it was about to leave. A. aboard                     B. board                             C. abroad                    D. on abroad  答案：A下列有关哺乳动物胚胎工程有关的叙述，正确的是（   ）A．采集到的精子和卵细胞相遇即可发生受精作用B．用于移植的早期胚胎不一定是由受精卵发育而来C．胚胎分割次数越多,产生的新个体也越多D．对同一胚胎的肝细胞核移植，产生的动物中雄性和雌性的概率各为1/2