When a researcher asks the question, "Have subjects been pre-selected so as to represent the extremes on the variable of interest?", she is concerned with which one of the following potential threats to internal validity?

A. Regression effect
B. Subject selection
C. Testing effect
D. Maturation

Why did separate government develop in ancient greece?

Which principle do modern democracies share with ancient athens? a. all people deserve equal rights. b. there should be no taxation without representation. c. people should vote on all matters that concern them. d. people should have a voice in government.

According to this map, which of these statements about cuban economic activity is true? a) coffee is not a valuable commodity in cuba. b) cattle ranching is found only in the western half of cuba. c) tobacco is grown in most areas of the country. d) manufacturing is limited to mostly the southern coast.