There ___________ 24 students in our class. [ ]
A. is
B. are
C. have
D. am
答案：B
Isn't it time you got down to _____ the papers?[ ]
A. mark
B. be marked
C. being marked
D. marking
在骨折部位发生的骨髓感染
A．局限性骨脓肿
B．创伤后骨髓炎
C．慢性骨髓炎
D．硬化性骨髓炎
E．急性骨髓炎
