胎头沿着骨盆轴前进的动作为（）。
A．胎头外旋转
B．胎头俯屈
C．胎头内旋转
D．胎头衔接
E．胎头下降
参考答案：E
Traffic conditions in Beijing ________ for decades. At first people only complained about jams during rush hours，but today every hour is rush hour.
A．is worsening
B．have worsened
C．worsened
D．have been worsening
常用最大剂量法为最敏感和首选方法的是
A．体外细胞毒性试验B．全身毒性试验C．皮肤刺激及皮内反应D．致敏试验E．遗传毒性试验
