Correct answer c)

Dr Zheng  has not suffered an acute cognitive decline.  His sensorium appears clear (that is, there is no clouding of his consciousness when you interact with him) so delirium seems unlikely.  There is no evidence of depression.  Acute stroke generally produces focal neurologic deficits and thus is unlikely to  be the cause of Dr Zheng’s presentation.  Although small vessel vascular disease could be a contributing factor, Dr Zheng does not have a lot of vascular risk factors and his CT did not show evidence of vascular brain disease.