下列影像学方法中哪种可行任意方位断层（）
A.螺旋CT
B.电子枪CT
C.MRI
D.SPECT
E.PET
参考答案：C
I have been told that the new law will come into _____ on January 1st next year. [ ]
A. effect
B. use
C. service
D. existence
采用乙炔切割或烧孔的钢轨，必须在（）内更换。
A、8h
B、12h
C、24h
D、3h
