常用抗癌药物按作用原理分为：____、____、____、生物碱类等。
参考答案：烷化剂类、抗代谢类药、抗生素类
The good situation came at last ____ we had been expecting in the past two years. [ ]
A. where
B. that
C. when
D. in which
《中华人民共和国动物防疫法》的立法宗旨是预防、消灭和控制畜禽疫病，提高畜禽健康水平。（）
