Which of the following is true regarding mild cognitive impairment (MCI)?
A. Seventy-five percent of Americans over the age of 60 are affected by mild cognitive impairment.
B. Mild cognitive impairment always progresses to Alzheimer's disease.
C. Mild cognitive impairment should be treated with cholinesterase inhibitors.
D. A patient who is affected by mild cognitive impairment has a more cognitive impairment than would be expected for their age, but it is not severe enough to be considered dementia.