Robert stands three times on a pair of scales within a period of 5 minutes. The first time he weighs 92 kg, the second time he weighs 102 kg and the third time he weighs 95 kg. His real weight is 86 kg. What is the matter with the scales?
A. The pair of scales is not reliable and not valid.
B. The pair of scales is reliable but is not valid.
C. The pair of scales is not reliable but is valid.
D. The pair of scales is reliable and valid.
Answer: A. The pair of scales is not reliable and not valid.