所有智能电能表（单相或三相，费控或非费控）均配置有（）。
A.485接口
B.USB接口
C.载波模块
D.红外接口
参考答案：A
食管支架置入术的适应证是（）
A.食管气管瘘
B.食管癌术后吻合口狭窄
C.原发性食管癌
D.心功能衰竭
E.肾衰竭
----Is John coming by train?
----He should, but he __________not. He likes driving his car.
[ ]
A. must
B. can
C. need
D. may.
