竞争性拮抗药具有下列特点（）
A. 对受体有亲和力
B. 对受体有内在活性
C. 可抑制激动药的最大效能
D. 当激动药剂量增加时，仍然达到原有效应
Only when we hurried to the airport__________the flight was cancelled.
A. we found
B. did we find
C. have we found
D. we have found
When ___________to zero degree centigrade, water will be changed into ice.
A. cooled
B. being cooled
C. having cooled
D. cooling
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