上颌右第二乳磨牙近中邻面深龋穿髓经根管治疗后，宜采取的治疗方法是

A．金属全冠
B．金属嵌体
C．树脂全冠
D．塑料全冠
E．牙体充填术

—Who's that boy reading in the garden? Is it David?  

—It ____be David. I saw him in the classroom just now.   [ ]

A. must    

B. can't      

C. may      

D. shouldn't