---Why didn't you answer my phone when I phoned you at about 11 p. m. yesterday?
---I ___________and failed to hear the phoneA.might have sleptB.must be sleepingC.might be sleepingD.must have been sleeping
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D解析本题可以采用排除法。问句中提供整个过程表示过去的行为。情态动词后接完成时表示对过去的猜测，故排除B、C。问句中有“at about 11 p．m．”具体的时间点，所以选D。