单选题According to the passage, why couldn’t PET and functional M. R. I. scans detect subtle changes in blood flow earlier?ABecause there is early oxygen transfer.BBecause they do not form their images quickly enough to follow such rapid changes.CBecause researchers control the changes in blood flow.DBecause early oxygen transfer gives the flow blood energy.
单选题
According to the passage, why couldn’t PET and functional M. R. I. scans detect subtle changes in blood flow earlier?
A
Because there is early oxygen transfer.
B
Because they do not form their images quickly enough to follow such rapid changes.
C
Because researchers control the changes in blood flow.
D
Because early oxygen transfer gives the flow blood energy.
参考解析
解析：
是非题。第五段第一句指出“血流中微妙变化的出现显然早于PET和功能性M R L扫描的探测”时提到，这两种技术lack sufficient resolution and do not form their images quickly enough to follow such rapid changes，对应选项B。
是非题。第五段第一句指出“血流中微妙变化的出现显然早于PET和功能性M R L扫描的探测”时提到，这两种技术lack sufficient resolution and do not form their images quickly enough to follow such rapid changes，对应选项B。
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