使用饲料添加剂应该遵守哪些原则？
参考答案：
（1）安全；
（2）有效；
（3）稳定；
（4）适口性好；
（5）对环境无不良影响。
海南省：琼
A．云南省：滇 B．黑龙江省：龙 C．江西省：鄂 D．甘肃省：肃
George is going to talk about the geography of his country, but I'd rather he ____ more on its culture. [ ]
A. focus
B. focused
C. would focus
D. had focused
