At Least 50 Percent of Adults Aged 80 Complete Fluid

At least 50 percent of adults aged 80 complete fluid and crystallized tests of intelligence and performance at rates similar to young people. This statement suggests _______.

A) extensive variability within age groups
B) that at least half of older adults have had increases in their IQ scores over time
C) that at least half of younger adults have higher IQ scores than the older adults
D) all of the above are suggested