Memory, they say, is a matter of practice and exercise.(1)_______________________.But even if you are successful,there are times when your memory seems to play tricks on you.Sometimes you remember things that really did not happen.One morning last week, for example,I got up and found that I had left the front door unlocked all night,yet I clearly remember locking it carefully the night before.Memory “tricks” work the other way as well.(2)_______________________.One day last month, for example,I was sitting in a barber shop waiting for my turn to get a haircut,and suddenly I realized that I got a haircut two days before at the barber shop across the street from my office.(3)_______________________.Stories about absent-minded professors have been told for years,and we never get tired of hearing new ones.Unfortunately, however, absentmindedness is not always funny.There are times when “tricks”of our memory can cause us great trouble.