以下有关前后对照试验的描述,错误的是:()
A. 比较节省研究样本量
B. 可以采用随机的方法决定试验药物和对照药物的先后顺序
C. 将试验药物使用前后的效果进行比较
D. 可以配合盲法
E. 两观察期间的洗脱期时间间隔不宜过短或过长
1. This text is mainly about a father’s ________.
A. interests
B.love for his children
C. lifestyle
D. achievements in life
The speaker _____for a moment, and then began to answer the question.
A. shook
B. paused
C. pressed
D. tripped
He suffered a serious _____in the car crash (猛撞), and died on the way to hospital.
A. injury
B. accident
C. fall
D. attack