He is very old, _____ he works like a young man.. [ ]
A. and
B. or
C. because
D. but
答案:D
SPECT的系统分辨率等于()。
A.固有分辨率1/2+准直器分辨率1/2
B.固有分辨率+准直器分辨率
C.固有分辨率2+准直器分辨率2
D.固有分辨率×准直器分辨率
E.固有分辨率/准直器分辨率
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