交叉反应是由于两种不同的抗原分子中具有（）
A.构象决定簇
B.不同的抗原决定簇
C.功能性决定簇
D.共同抗原决定簇
E.连续性决定簇
参考答案：D
The number of people invited ______ fifty, but a number of them ______ absent for different reasons.
A．were; was
B．was; was
C．was; were
D．were; were
