Marty is a 71-year-old patient with a family history of Alzheimer's disease. He has been participating in an Alzheimer's disease research study for the past 5 years. In the study, he has been categorized as "prodromal" based on biomarker results and neuropsychiatric testing. Which of the following biomarker results are indicative of Alzheimer's disease?
a. Decreased CSF tau and decreased CSF amyloid beta protein
b. Decreased CSF tau and elevated CSF amyloid beta protein
c. Elevated CSF tau and elevated CSF amyloid beta protein
d. Elevated CSF tau and decreased CSF amyloid beta protein
