Astudy of widows and widowers found that 9 percent were slow to recover, functioning poorly even at 18 months. by four years after the death, however, they functioned almost as well as they had before the death. this slow and incomplete recovery suggests that they:

- Experienced complicated grief.

Explanation:

Complicated grief is described as the intense and complicated mourning over a loss. Such grief invokes adjustment disorders like trauma, severe depression, etc. due to distressed and disturbed emotional state and anxious behavior. This kind of grief is often characterized by delayed or extended grief that mars the usual functioning and often resulting in suicidal attempts( it becomes difficult to recover.

As per the question, the slow and incomplete recovery even after four years after the death exemplifies that they experienced 'complicated grief' which makes it difficult for them to overcome due to intense depression and anxiety lying inside them. Hence, they experience an inability to recover due to 'complicated grief'