At what age do children begin to show an ability to deceive others?

In which of the following countries are dizygotic twins most common?

Canada Scotland United States Nigeria

Willis and Schaie's longitudinal study on cognitive performance allowed for the comparisons of participants ____

a. to a larger mainstream group, who possessed similar characteristics b. current performance on cognitive tasks to their performance years earlier c. to others in various parts of the world and geographical locations d. current performance to others who are at a different developmental stage