类毒素
参考答案：外毒素经0.3%-0.5%甲醛溶液于37℃处理后（1分），丧失毒性，但仍保持抗原性，称类毒素。（1分）
Read and choose.（读句子，选择恰当的答语）
1. What do you usually do on the weekend? [ ]
A. I often play football.
B. I played football.
2. What do you do? [ ]
A. I usually go shopping.
B. I am a teacher.
3. When do you get up?[ ]
A. At 6:00.
B. Sure.
4. What do you do on the weekend? [ ]
A. It's great!
B. Sometimes I climb mountains.
肝动脉提供肝脏全部血液供应的（）
A.15%～19%
B.20%～30%
C.31%～40%
D.41%～50%
E.51%～60%
