Cet-4-1.19-Exercise 02The study, which followed more than 2,000 healthy adults between the ages of 18 and 60, found that certain mental functions – including measures of abstract reasoning, mental speed and puzzle-solving – started to dull as early as age 27. What does the new study find about mental functions?

A. They reach a peak at the age of 20 for most people.
B. Some of them begin to decline when people are still young.
C. They are immeasurable.
D. They are unpredictable.