固体熔化时，必须破坏非极性共价键的是[ ]
A．冰
B．晶体硅
C．溴
D．二氧化硅
答案：B
The performance ______ nearly three hours, but few people left the theatre early. [ ]
A. covered
B. reached
C. played
D. lasted
消化性溃疡所引起的疼痛最具有特征性的是（）
A.中、上腹疼痛
B.饥饿样痛
C.反复发作性痛
D.节律性痛
E.长期作痛
