单项选择题 Of the various schemes that have been proposed to model how gene transcription might work in the living body, those involving actual physical contact between enhancers and genes remain （）, owing to an absence of direct evidence.

单项选择题 An excellent philatelist can detect a forged （） with a single glance, for a true specimen bears markings and characteristics, without exception, that the（）invariably lacks.

单项选择题 The result of this biochemical test has caused an uproar, and ever since its publication, researchers have been full of responses of （） quality: whereas some deal with the test's implications in a calm manner, others sound alarms.