He bought two____ (box) of chocolate at the store.
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Friendship falls apart because of lack of opportunity___________.
A. to meet.
B. to hang out.
C. to connect.
D. All of the above.
People go to big cities for ______________.
A. Jobs.
B. Opportunities.
C. Peace.
D. A and B.
结构中含有四个手性中心的药物是：
A. 阿莫西林
B. 青霉素
C. 头孢羟氨苄
D. 头孢克洛
E. 头孢噻肟钠
药物的亲脂性与生物活性的关系最正确的描述是
A. 增强亲脂性，有利吸收，活性增强
B. 降低亲脂性，不利吸收，活性下降
C. 适度的亲脂性有最佳活性
D. 增强亲脂性，使作用时间缩短
E. 降低亲脂性，使作用时间延长
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